Revert "Workaround bogus TreeMap Comparators."

This was a temporary workaround for app compatibility in Android N.

Bug: 27913360
Test: cts-tradefed run cts -p android.core.tests.libcore.package.libcore

This reverts commit 78562a12.

Change-Id: Ib03ee04d17da5d2b8e943c2da9b7351f852ce716