Add an API to SBDebugger class:

    bool SBDebugger::DeleteTarget(lldb::SBTarget &target);

which is used in the test tearDown() phase to cleanup the debugger's target list
so that it won't grow larger and larger as test cases are executed.  This is also
a good opportunity to get rid of the arcane requirement that test cases exercising
the Python API must assign the process object to self.process so that it gets
shutdown gracefully.  Instead, the shutdown of the process associated with each
target is now being now automatically.

Also get rid of an API from SBTarget class:

    SBTarget::DeleteTargetFromList(lldb_private::TargetList *list);

llvm-svn: 133091