Do not pass junit.jar to vogar.

Not needed after https://android-review.googlesource.com/#/c/150563.
Also dex2oat now complains about duplicated classes, and fallbacks
to the interpreter if it sees any. Since vogar has its own junit,
dex2oat was complaining.

Change-Id: I579feb0b1a049af3fba664fd2d86c67c66c8eae1