lakitu: Update kernel ebuild to remove unnecessary ebuild variables.

As uprev bot will be in-place for both presubmit and official builds,
manual uprevving is not needed. Therefore, it is safe to remove
CROS_WORKON_BLACKLIST and other not required workon variables.

BUG=b/169936343
TEST=presubmit
RELEASE_NOTE=None

Change-Id: If175e2fc2ccbe28173c4de0a606cb1d41e23f60c
2 files changed