Fix PR33878: BasicAA incorrectly assumes different address spaces don't alias

Fix PR33878: BasicAA incorrectly assumes different address spaces don't alias
Remove code that assumed that a nullptr of address space != 0 couldnt alias with a non-null pointer. This is incorrect, since nothing can be concluded about a null pointer in an address space != 0.
This code was written before address spaces were introduced

Differential Revision: https://reviews.llvm.org/D37518

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@312648 91177308-0d34-0410-b5e6-96231b3b80d8