NICE...This is a good workaround, thanks for this!  

I could imagine, as ToystoryLab pointed out, if I had multiple keyed instances it will be quite cumbersome to rely on the workaround, it optimally should be delete-able on the timeline itself. 
ie- if you have several instances, you shouldn't be forced to delete all instances because you want to take away one instance. 
Although, an additional workaround could then be to add an independent instance in the Post Effect list, for each time-lined instance.  That way, if you had 5 instances, and if you wanted to delete #3, you just delete the 3rd instance in the list, thus preserving the other 4.  But, this agreeably will be unnecessarily complex and problematic.

To your thought, it indeed seems the HDR slider stuff (ie- IBL strength, Exposure, etc) is in fact deletable on the timeline. 
But when you add an actual Post Effect it cannot be deleted.
So, yes, you can modify the HDR settings, ie - set Bloom amount on frame 100 to max, and then go and later delete that key on frame 100.
But if you add a Post Effect LUT, and then say change the amount of this LUT on frame 100, you cannot delete that key on the timeline, it is greyed out.  You are stuck with it, unless deleted from the Post Effect list as Wires pointed out

Keys in timeline from here CAN be deleted


Keys in timeline from here can NOT be deleted



Regards!
TonyD

Another workaround, is to simply override the key you are trying to delete. Drag the very first frame key over the key you are trying to delete. And then, when key is overridden, drag that key back to frame one - Done! 

wires (1/8/2018)

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All of the post effects can be deleted simply by selecting them in the Effects list panel and then clicking on the "Delete" icon.

 I have always simply moved the LUT/HDR keyframes using the mouse where I want to on the timeline, or just hit the 'delete' key to remove them, so I have had no issues here having not opposite clicked on the mouse to delete keyframes.   ~V~

       Val RogueAnanda

HDR - Yes
LUT - No
Anything under "Effect" cannot be deleted regardless (after last update I think). Not with right mouse click nor with delete keyboard key as Tony discovered. Did you try it lately on IC 7.2?

And no Curve Presets are available either for Effects...


Here is a quick video on Effect keys with override option

At minimum it would be more intuitive if you would right-click and you could delete it, because otherwise it makes the user wonder if there's some functional reason why it shouldn't be able to be deleted. 
Thinking out loud, perhaps this is connected to the earlier notes by Shadoesword in this thread about copying and pasting keys for individual bones, and how the introduction of the curve editor changed some of the workings. 

@4u2ges - in the 7.1 issues thread, you brought up that we no longer had the ability to set curve presets from the key root.  
Does that issue still remain, or did you find a workflow that works okay?  Just was remembering that.

No Tony, the problem still remains. Nobody entered this particular one into FT. But I kind of used to it... Geee, all I do is get used TO...

But I found out how to really delete the Effect keys with keyboard "delete". Whatever you do, do NOT right mouse click on that key. If you click on it once and grayed out menu showed up, "Delete" key would stop working. BUT, if you just right mouse click on ANY other working key (like HDR) after that, then you may delete an Effect key with the "Delete" keyboard key... Now just get used to that :)

4u2ges - I have no problems deleting effect keyframes on my timeline in 7.2 simply using the 'delete' key - Here is a quick video of me doing this on my timeline to show that it works for me..   ~V~

       Val RogueAnanda

Right Val, and I found the source of the problem later on with "delete" key (post above). If you do right mouse on effect key once, the "delete" would stop working, until you do right mouse click again on some key other than effect... weird!

Ahhh...
Now having read what 4u2ges just posted, you were never right-clicking the mouse button, and thus, you encountered no issue....
Whereas, I was always right-clicking to try to get this to work, and then even if I would next attempt a keyboard-delete, I would find it didn't work.
Okay great, like you show in your video, and like 4u2ges described, a workaround is if you DO NOT use the right mouse button, you are good to go.   I can as well also delete now if not having right-clicked.

ISSUE - A right-click on a Post-Effect timeline key locks out that post effect key from being able to be deleted. 
Workaround involves using any other means to delete the post effect, including keyboard delete key, without ever using a mouse-button right-click on that key.
  
In a way, the right mouse button winds up being the wrong mouse button to press.
Think about that for a moment....
.