misc: Delete the critical path annotation code.

misc: Delete the critical path annotation code.

This code was at least a little Alpha specific, and now that Alpha is
gone it can no longer be compiled. We could either fix it up to work
with other/all ISAs or delete it, and the consensus was to delete it. It
could potentially be revived in the future by retrieving it from version
control.

Change-Id: Ied073f2b9b166951ecba3442cd762eb19bc690b3
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/32954
Reviewed-by: Steve Reinhardt <stever@gmail.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>