Enable code item deduping

Dedupe code items if they have the same contents, this is safe
because of the fixed quickening logic.

Removed duplicate code items in ManyMethods that caused the startup
methods section to be empty in dex2oat_test.

To avoid errors related to quickening and compilation of shared code
items, quickening is currently disabled for shared code items.

Bug: 63756964
Test: test-art-host

Change-Id: I7c62eb746785d787c5269effd396f7be4859d3a6