Sanitizers do not create a log file when no defects are found. Therefore,
it is currently impossible for ctest_memcheck to set both
`CAPTURE_CMAKE_ERROR` and `RETURN_VALUE` to zero.
With defects, `CAPTURE_CMAKE_ERROR`=0 and `RETURN_VALUE`=-1, as expected.
With no defects, `CAPTURE_CMAKE_ERROR`=-1 and `RETURN_VALUE`=0.
A more-specific error message is always displayed earlier in the
output if any real error occurred. This final summary message
is distracting to readers searching through the output for the
word "error". Simply drop it.
The Dummy*-stderr.txt files were needed only to match platform-specific
memcheck tooling output and verify that stderr is otherwise empty. Now
that the RunCMake infrastructure knows how to strip such lines before
matching, we can simply drop these files and use the default empty
string match.
