test_strings:  Remove string tests that exercise asserts.

Since unit tests are run with DO_CRASH, those tests were causing
the test to fail.

Tested-by: George Joseph
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Merged revisions 427354 from http://svn.asterisk.org/svn/asterisk/branches/11
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Merged revisions 427355 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/branches/13@427356 f38db490-d61c-443f-a65b-d21fe96a405b