Remove old diagnostic crash reports.

We aren't actively investigating these, and they're generating
crash reports without telling us new information.  Remove the old
diagnostics.

This basically reverts the following CLs from 575245:
https://codereview.chromium.org/1613453002/
https://codereview.chromium.org/1618063003/
https://codereview.chromium.org/1643673002/
https://codereview.chromium.org/1656603002/

(I left https://codereview.chromium.org/1581193002/ in place,
since it seems useful as a safeguard.  I also left
https://codereview.chromium.org/1624413002/ because it seems
to be indicative of a problem we might not be catching.)

BUG=575245
TEST=Fewer crash reports
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_site_isolation

Review-Url: https://codereview.chromium.org/2572573003
Cr-Commit-Position: refs/heads/master@{#470669}
9 files changed