Revert [SROA] Enhance SROA to handle `addrspacecast`ed allocas

This reverts r363711 (git commit 76a149ef)

This causes stage2 build failures, e.g.:
http://lab.llvm.org:8011/builders/clang-x64-windows-msvc/builds/132/steps/stage%202%20build/logs/stdio
http://lab.llvm.org:8011/builders/ppc64le-lld-multistage-test/builds/87/steps/build-stage2-unified-tree/logs/stdio

llvm-svn: 363718