dx: Update prebuilts with a version that is built for 1.7

Some unbundled branches do not support class v52 version files
and would barf when trying to load classes from dx.jar.

Since dx does not use any v52 features, replace it with a v51
binary.

Change-Id: I367ee23a853e2905fd6f6461acd34d9a13ba03d0
1 file changed