[lldb] Don't search for system specific strings in assert.test

Commit 6bc1e69de270db8d7191200f54158e4192f997ba changed the search string
to also check for the generated strings that surround the plain assert:

    Assertion `false && "lldb-test assert"' failed
                                         ^^^^^^^^^

This causes the test to fail on setups where the generated assert message
looks different. E.g., on macOS the generated message looks like this:

    Assertion failed: (false && "lldb_assert failed"), function lldb_assert

This reverts the old behaviour of just checking for the actual string we
have inside LLDB.

GitOrigin-RevId: 3c95bdf9fa35f0fe2143ea859b624c8f09513adb
1 file changed