[test] Delete some xfailed lldb-mi tests

[test] Delete some xfailed lldb-mi tests

This is a first pass at removing some lldb-mi tests which have been
xfailed and unmaintained for a while. We have open PRs for most of these
tests already. I've opened up the following additional PRs:

  llvm.org/PR36739 - lldb-mi driver exits properly
  llvm.org/PR36740 - lldb-mi -gdb-set and -gdb-show
  llvm.org/PR36741 - lldb-mi -symbol-xxx

The motivation here is to address timeout and pexpect-related issues in
the test suite. This was discussed on lldb-dev in the thread: "increase
timeout for tests?".

After this change, the lldb-mi tests seem to be in better health (on
Darwin at least). I consistently get:

$ ./bin/llvm-dotest -p TestMi
===================
Test Result Summary
===================
Test Methods:        101
Reruns:                0
Success:              88
Expected Failure:      0
Failure:               0
Error:                 0
Exceptional Exit:      0
Unexpected Success:    0
Skip:                 13
Timeout:               0
Expected Timeout:      0

llvm-svn: 327552