Revert "Compare method bodies for changes in inc optimizer."

Benchmarks have shown that the method comparisons introduced in the
reverted commit actually make incremental compilation slower. We need
to postpone this optimization (see #1017).

This reverts commit 1151b96682aab8151fa9f1b17f17ae7142a49ffb.
Merge pull request #1018 from gzm0/revert-cmp-tree

Revert "Compare method bodies for changes in inc optimizer."