Revert r149311 which failed to compile.

Revert r149311 which failed to compile.

Original log:

Convert ProgramStateRef to a smart pointer for managing the reference counts of ProgramStates.  This leads to a slight memory
improvement, and a simplification of the logic for managing ProgramState objects.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@149336 91177308-0d34-0410-b5e6-96231b3b80d8