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>

src/base/SConscript

@@ -28,9 +28,6 @@
 
 Import('*')
 
-if env['CP_ANNOTATE']:
-    SimObject('CPA.py')
-    Source('cp_annotate.cc')
 SimObject('Graphics.py')
 Source('atomicio.cc')
 GTest('atomicio.test', 'atomicio.test.cc', 'atomicio.cc')