[Test] rewrite inline_nossp.ll

While adding remark based tests in D104944, I noticed that the tests
that we were passing were passing for the wrong reason. They were
passing because the dynamic allocas were preventing inlining, not the
code I added in D91816.

Rewrite and simplify the test. Add remark based checks to validate we're
preventing inline substitutions for the right reasons.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D104958