Prune some LeakSanitizer suppressions.

Remove some suppressions which no longer match. Among them a bunch of
suppressions related to Blink bindings, which I assume is related to Oilpan
deployment.

Also, improve a comment in the suppressions file.

BUG=99304, 67378, 189170, 328552, 317965
TBR=glider@chromium.org

Review URL: https://codereview.chromium.org/184103009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254378 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254378