MergeFunctions Pass, removed unused methods from old implementation.

    
Patch removed next old FunctionComparator methods:
    * enumerate
    * isEquivalentOperation
    * isEquivalentGEP
    * isEquivalentType 
    
This patch belongs to patch series that improves MergeFunctions
performance time from O(N*N) to O(N*log(N)).

llvm-svn: 211444