[web-tests] Remove `expectations` arg from `TestResultSink.sink()` (1/n)

Callers pass the same object of all `TestExpectations` every time [0],
so just construct `TestResultSink` with a reference to it.

This is a no-op refactor before unifying `run_{web,wpt}_tests.py` test
result reporting.

[0]: https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/tools/blinkpy/web_tests/controllers/web_test_runner.py;l=93;drc=1f6f15344f369a5728ba9599949e7f52e0af8ad0;bpv=0;bpt=0

Bug: 41491345
Change-Id: I89277262e42a23c27ee000f5afebdf604b6575d6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6182931
Reviewed-by: Weizhong Xia <weizhong@google.com>
Commit-Queue: Jonathan Lee <jonathanjlee@google.com>
Cr-Commit-Position: refs/heads/main@{#1409106}