Revert "runtime: Mmap uncompressed dex files (in zip) as clean memory"

Getting on the bots:
+ERROR: Memory mapping for /data/run-test/test-6248/071-dexfile-map-clean-ex.jar is unexpectedly dirty
+Private_Dirty:         4 kB


Bug: 27650033

This reverts commit 19e5f834.

Change-Id: I833ef95401187b764d336ab4558936c63678061c