[flang] Runs FIR SimplifyRegionLitePass pass after calling the inliner

In flang pipeline, the inliner calls createCanonicalizerPass with the region
simplification disabled. The inliner pass does canonicalization even if
no inlining happens. After canonicalization, FIR lite region simplification
must be called to get rid of unreachable regions.
This code exposes the need to run SimplifyRegionLitePass after the inliner is
called with FIR pipeline.

Differential Revision: https://reviews.llvm.org/D130484