[mlir][sparse] move conversion test back to original CHECK testing

Rationale:
The silent exit(1) gives little clues on where the error occurs on failure
and may even be confusing at first. The CHECK testing of all computed values
and indices may be a little bit more elaborate, but it directly pinpoints
where errors happen if they occur. This style is also consistent with
the other tests, which I actually prefer.

Reviewed By: bixia

Differential Revision: https://reviews.llvm.org/D112688