Remove :--foo syntax from CSSSelectorParserTest

:--foo is the deprecated syntax for css custom state and I am about to
disable it by default, so I am replacing it with the new syntax in this
test. Some of the test cases already have the new syntax in there in
which case I am just deleting the usage of the old syntax.

Bug: 41486953
Change-Id: I4bccf3e7d2e15271186438a8a202d5f31daf83eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5584183
Commit-Queue: Di Zhang <dizhangg@chromium.org>
Commit-Queue: Joey Arhar <jarhar@chromium.org>
Auto-Submit: Joey Arhar <jarhar@chromium.org>
Reviewed-by: Di Zhang <dizhangg@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1308382}