- All testcase/testsuite/variant generator subclasses renamed to
  just TestCase/TestSuite/VariantGenerator since they're private
  implementation.
- All `testcase` variables renamed to `test` to not conflict with
  a module name.
- No more two statements in the same line.
- Removed some unused testsuite methods.

Bug: v8:6917
Cq-Include-Trybots: master.tryserver.v8:v8_linux_noi18n_rel_ng
Change-Id: I7710f3419f738a5f9ddca73765dd2cad2e35b952
Reviewed-on: https://chromium-review.googlesource.com/823964Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michał Majewski <majeski@google.com>
Cr-Commit-Position: refs/heads/master@{#50076}