Remove inactive contributors (cira and mnita) and add ftang and jshin.

Change-Id: Ibd1e4f11553b78e1cd938a7ce8958fe5341829d2
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1872540Reviewed-by: Frank Tang <ftang@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64484}