SIL: Remove the bump pointer allocator for zombie function names from SILModule.

It's not needed because the names are stored in the ZombieFunctionTable anyway (this table was added later).

include/swift/SIL/SILModule.h

@@ -171,9 +171,6 @@ private:
   /// but kept alive for debug info generation.
   FunctionListType zombieFunctions;
 
-  /// Stores the names of zombie functions.
-  llvm::BumpPtrAllocator zombieFunctionNames;
-
   /// Lookup table for SIL vtables from class decls.
   llvm::DenseMap<const ClassDecl *, SILVTable *> VTableMap;