Explicit dependency on hostdex classes.jar.

Previously for hostdex Java libraries, we set up dependency on only
javalib.jar, which in turn is dependent on classes.jar.
But when jack is enabled there is no dependency of javalib.jar on
classes.jar. In commit b4c49cba classes.jar was universally added to
all host java library dependencies. That's unnecessary.

This change adds explicit dependency on classes.jar only for hostdex
modules.

On the other hand, if we switch checked module to $(full_classes_jack),
like what we did in commit 8bc90fd2, we won't need this to fix jack
build either, because classes.jar isn't needed when you run checkbuild.

Change-Id: I92c0e4d621d266f6e6914ab2b4f20e5531af070f