Add a call to SBDebugger:Destroy() at the end of the self-hosted

version of this script.  We picked up a bug at some point in March
where scripts that fail to call SBDebugger::Destroy() will crash
in the Debugger C++ dtor.  I want to track the change down which
introduced the change - but this script should be calling
SBDebugger::Destroy() in the first place, so do that.

llvm-svn: 233779