Revert "Sync 4.6 toolchain in prebuilt."

This reverts commit 612bdcd38128a68729bb73ba4c36700ad6b091bc.

Google didn't change this, so why are we changing this. You're using a custom
toolchain, your problem! Not ours....

https://github.com/android/platform_manifest/blob/android-4.4_r1.2/default.xml#L392

Change-Id: Ie3614115ec9b260c936210053fea84e9a160bd42
Signed-off-by: Lokesh Chamane <lokesh.c703@gmail.com>