Linker: Clarify test/Linker/type-unique-odr-a.ll, NFC

Split up the long RUN and clarify the CHECK lines:

  - Explicitly confirm there are no other subprograms inside of "A".

  - Remove checks for "bar" and "baz", which were just implicitly
    checking that there were no other subprograms inside of "A".

This prepares for adding a RUN line which links the two files in the
opposite direction.

llvm-svn: 266543