[wptrunner] Remove `chrome` port and expectations

Currently, the WPT infrastructure supports both content shell and chrome
coverage on Linux simultaneously. The plan now is to open up chrome as
an option on macOS and Windows, with the caveat that each WPT can only
target one binary or the other. This will keep the number of
expectations manageable and minimize the amount of redundant coverage.

This CL:
* Removes harness support for the `linux-chrome` option, since this will
  be decided at the test level.
* Renames `*-expected.txt` files out of the obsolete `linux-chrome`
  directory as needed.
* Removes ChromeTestExpectations, with any necessary wdspec test
  expectations moved to TestExpectations.

Bug: 328079854
Change-Id: I205197b038e6441773b2d7307a83e8d5da3837a0
Cq-Include-Trybots: luci.chromium.try:linux-blink-rel
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5747069
Reviewed-by: Weizhong Xia <weizhong@google.com>
Commit-Queue: Jonathan Lee <jonathanjlee@google.com>
Reviewed-by: Thomas Anderson <thomasanderson@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1338757}