[test][LoopUnroll] Cleanup FullUnroll.ll

[test][LoopUnroll] Cleanup FullUnroll.ll

This is in preparation for enabling proper handling of optnone under the
NPM. Most optimizations won't run on an optnone function.

Previously the test would rely on lots of optimizations to optimize the
IR into a simple infinite loop. This is an optnone function, so clearly
that shouldn't be the case.

This IR was found by printing the module before the LoopFullUnrollerPass ran.

Reviewed By: asbirlea

Differential Revision: https://reviews.llvm.org/D85578