[MLIR] NFC clean up loop tiling test cases

Summary:
Improve the checks and drop redundant ones. Rename the outlined maps
better.

Reviewers: andydavis1, nicolasvasilache

Subscribers: mehdi_amini, rriddle, jpienaar, shauheen, antiagainst, nicolasvasilache, arpith-jacob, mgester, lucyrfox, aartbik, liufengdb, Joonsoo, grosul1, frgossen, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D78514