Make some tests LLVM-optimization agnostic and remove some others that were beyond value/repair

Several of these tests (the two deleted, and the one removal edit) were
relying on the optimizer to collapse things to test some frontend
feature. The tests were really old and features seemed amply covered by
other parts of the test suite, so I just removed them.

If anyone thinks they're valuable enough to keep/fix, we can play around
with that, for sure.

(inspired by r252872)

llvm-svn: 253114