Since we have only unittests that are under GoogleTestSuite there
is no need to keep it as a default suite and we can make it
specific for unittests.

Bug: v8:6917
Change-Id: Ie2d57342773f228dea72184ab0f2abfc9d2daa70
Reviewed-on: https://chromium-review.googlesource.com/819253
Commit-Queue: Michał Majewski <majeski@google.com>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50011}