Modules: Remove an invalid check in unit tests for r298278

This is a fixup for the unit tests from r298278 (originally r298165).

Since the buffer that RawB2 pointed at was later deleted, a new call to
getBuffer may very well return a buffer at the same/old address.  Which is
fine.  Just delete the spurious check.

A Windows bot was occasionally hitting this in practice:
http://lab.llvm.org:8011/builders/llvm-clang-lld-x86_64-scei-ps4-windows10pro-fast/builds/7086

llvm-svn: 298414