remove plugin exception restoration code

First part (this CL): remove only caller.

Back in the days of Flash 9, we added this code to restore
the unhandled exception handler which flash sometimes stole.

Since flash 10 this is no longer true, and now it is not possible
in chrome to use old flashes so this code just adds complexity
for no good reason.

TBR=jam
BUG=none

Review URL: https://codereview.chromium.org/122553003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242789 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242789