Remove @chromium.org accounts from OWNERS.

Remove @chromium.org accounts from OWNERS.

Android now also uses OWNERS files for commit approval in Gerrit (see
b/33166666). But they don't recognize the @chromium.org accounts. We
shouldn't need them for Chromium if we just use our @google.com
accounts, so they can be removed. Also use full account names instead
of aliases.

Bug b/63147516

Change-Id: Ic5dfab1aad0025ec20f5a0f79b612c893fece8fc
Reviewed-on: https://swiftshader-review.googlesource.com/10548
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
Tested-by: Nicolas Capens <capn@google.com>