Switch target java library dependency file from javalib.jar to classes.jar

Previously, any target Java code that depends on framework.jar has to
wait for the library's javalib.jar.
To build javalib.jar we have to run dx, which is quite slow.
Actually when code links against framework.jar, only classes.jar is
needed.
This improves the potential parallelism of the build system.

Change-Id: I82c5926ef282a3a6096bbf49b54ef4f2a0c2c0e7