Remove alloc_zeroed optimisation

It causes some weird UB-ey interaction in rustc_data_structures

Author: nagisa

lib/Analysis/MemoryBuiltins.cpp

@@ -77,7 +77,6 @@ static const std::pair<LibFunc, AllocFnsTy> AllocationFnData[] = {
   {LibFunc_strndup,             {StrDupLike,  2, 1,  -1}},
 
   {LibFunc_rust_allocate,       {MallocLike,  2, 0,  -1}},
-  {LibFunc_rust_allocate_zeroed, {MallocLike,  2, 0,  -1}},
   {LibFunc_rust_reallocate,     {ReallocLike,  4, 2,  -1}}
   // TODO: Handle "int posix_memalign(void **, size_t, size_t)"
 };