Revert "Add the beginning of hover-trigger for pop-ups"

This reverts commit cdbdb4520d6be65fdb04fc85aea5d12953f1a1da.

Reason for revert: Suspected cause of 1344436

Original change's description:
> Add the beginning of hover-trigger for pop-ups
>
> This CL adds the 'hoverpopup' attribute, to go along with the other
> invoking attributes (togglepopup, showpopup, hidepopup). This attribute,
> when places on *any* element, triggers a pop-up when hovered. With this
> CL, it is always triggered after a fixed 100ms delay, but that will be
> made configurable via CSS in subsequent CLs. There is also no "hide"
> trigger when any element is de-hovered - again that will be added
> later.
>
> See this spec discussion:
>  openui/open-ui#526 (comment)
>
> Bug: 1307772
> Change-Id: I7af88dad9efa015f833843ea76bed41b4aa42c4b
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3759184
> Reviewed-by: David Baron <dbaron@chromium.org>
> Auto-Submit: Mason Freed <masonf@chromium.org>
> Commit-Queue: Mason Freed <masonf@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1024141}

Bug: 1307772, 1344436
Change-Id: I65a1e36ead974e887c37b6a90ff6504fdaa45d71
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3760676
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Theodore Olsauskas-Warren <sauski@google.com>
Owners-Override: Theodore Olsauskas-Warren <sauski@google.com>
Cr-Commit-Position: refs/heads/main@{#1024173}