Go back to BSD grep for now.

PCRE grep isn't POSIX enough (BREs vs EREs).

Bug: http://b/111849261
Bug: https://bugs.exim.org/show_bug.cgi?id=2294
Test: N/A
Change-Id: I3eae7f2c50e2fa65702aba3efea73b915621d16e
1 file changed