DAG: Remove redundant finalizeLowering call

9cac4e6d/D32628 intended to eliminate
this, and move all isel pseudo expansion to FinalizeISel. This was a
bad rebase or something, and failed to actually delete this call.

GlobalISel also has a redundant call of finalizeLowering. However, it
requires more work to remove it since it currently triggers a lot of
verifier errors in tests.