[SROA] Remove incorrect assertion

Confirmed with aprantl, this assertion is incorrect - code can get here (for example 80-bit FP types) and if it does it's benign. This is exposed by a completely unrelated patch of mine, so stop the compiler falling over.

Original differential: http://reviews.llvm.org/D16187
aprantl's advice to remove assertion: http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20160815/382129.html

llvm-svn: 279454