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.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@174692 91177308-0d34-0410-b5e6-96231b3b80d8