[Instrumentation] Remove unused variable 'DL' in MemProfiler.cpp (NFC)

llvm-project/llvm/lib/Transforms/Instrumentation/MemProfiler.cpp:375:21:
 error: unused variable 'DL' [-Werror,-Wunused-variable]
  const DataLayout &DL = I->getModule()->getDataLayout();
                    ^
1 error generated.