Revert "Have InstCombine call SipmlifyCall when handling calls. Test case included."

This reverts commit 3854a5d90fee52af1065edbed34521fff6cdc18d.

This causes a clang unit test to hang: vtable-available-externally.cpp.
<rdar://problem/12898191>

Added a summary for NSMutableAttributedString
In the process, converted formatters for other NSString-based classes over to C++ code