Make lldb-mi handle only MI commands

Summary:
Previously lldb-mi can also act as a driver like normal lldb. It needed a lot
of redundant code in the lldb-mi for that. I think that if a user wants command
line lldb driver then he/she should use the lldb for it. This change will cleanup
the code a lot. When this change goes in, it will allow us to remove some more
redundant code too.

All tests pass on Linux. Did some sanity testing on command line and with eclipse.

Reviewers: ki.stfu

Reviewed By: ki.stfu

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D8381

llvm-svn: 232621