Remove XMLHttpRequestCrossOriginWithCredentials use counter

The data was used in https://github.com/whatwg/fetch/issues/251, but
we don't need it any more.

Bug: 602925
Change-Id: I529e30057e9ce9265a1eda4edf424cffde76034d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1602534
Commit-Queue: Yutaka Hirano <yhirano@chromium.org>
Reviewed-by: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658440}
3 files changed