Use java prebuilts

Point the make java variables at JDK prebuilts in
prebuilts/jdk/jdk8, add them to the path, and clean up
some old overrides.

Reapplies Ibbeb30fab96e45aedd5bb6d710d1170f85789982 after updating
some more manifests to include the prebuilts.

Bug: 62956999
Test: m -j checkbuild
Change-Id: I9e27aa5cb04d1ed09e43b798e5d654843afc000f
(cherry picked from commit 19317509)