[ScopedTaskEnvironment] Remove deprecated MOCK_TIME MainThreadTypes

All callers have been migrated to TimeSource::MOCK_TIME.

Also drastically reduced the number of ScopedTaskEnvironmentTests from
86 to 34 by getting rid of redundant/overkill instantiations of all
tests under all modes and replacing them by a few that provide the
same coverage.

R=fdoray@chromium.org
TBR=satorux@chromium.org
for chrome/browser/chromeos/android_sms/android_sms_app_setup_controller_impl_unittest.cc

Bug: 946657
Change-Id: I937f0b465ea6c75e087211c0ab210b6966f5ec92
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1704362
Commit-Queue: Gabriel Charette <gab@chromium.org>
Commit-Queue: François Doray <fdoray@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Auto-Submit: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#678701}