[polly][ScheduleOptimizer] Use IslMaxOperationsGuard helper instead of explicit restoration (#79303)

To fix long compile time issue of Schedule optimizer, patch #77280 sets
the upper cap on max ISL operations. In case of bailing out when ISL
quota is hit, error handling behavior was restored manually. This commit
replaces the restoration code with IslMaxOperationsGuard helper and also
removes redundant early return.

GitOrigin-RevId: 0f33c54854c4c7ef73ec56a881f63089c504a7bf
2 files changed