Remove redundant code from lldb-mi.

Summary:
After recent changes, some code has become redundant. This revision tries to remove
the un-used code and tidy up the rest.

Following 4 files have been removed. I have updated CMake files and checked that it builds
fine on Linux and Windows. Can somebody update the xcode related file accordingly?

tools/lldb-mi/MICmnStreamStdinLinux.cpp
tools/lldb-mi/MICmnStreamStdinLinux.h
tools/lldb-mi/MICmnStreamStdinWindows.cpp
tools/lldb-mi/MICmnStreamStdinWindows.h

Reviewers: clayborg, ki.stfu

Reviewed By: clayborg, ki.stfu

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D7834

llvm-svn: 230345