Remove some known_crashes.txt entries that are no longer needed. - 72796, 83674 and 83676 have not occurred recently (as far as back as we have builder logs) - 83657 has been fixed BUG=72796,83657,83676,83674 TEST=no [email protected] Review URL: http://codereview.chromium.org/7523034 git-svn-id: svn://svn.chromium.org/chrome/trunk/src/chrome/test/data/reliability@94805 0039d316-1c4b-4281-b951-d872f2087c98