[3.13] gh-108297: Update crashers README for test_crashers removal (#121476)

Update Lib/test/crashers/README for test_crashers removal
(cherry picked from commit 59be79ae60073f7b6bdf6ce921560c279937e4ab)

Co-authored-by: Alyssa Coghlan <ncoghlan@gmail.com>
1 file changed