TargetAsmInfo::getAddressSize() was incorrect for x86-64 and 64-bit targets

TargetAsmInfo::getAddressSize() was incorrect for x86-64 and 64-bit targets
other than PPC64. Instead of fixing it, just remove it and fix all the
places that use it to use TargetData::getPointerSize() instead, as there
aren't very many. Most of the references were in DwarfWriter.cpp.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42419 91177308-0d34-0410-b5e6-96231b3b80d8