Fix host java doc by referring to the correct classpath.

In droiddoc for host, we don't generate classes.jar for
LOCAL_JAVA_LIBRARIES. Switch to refer to the installed jar file instead.
This is consistent with how LOCAL_JAVA_LIBRARIES for host is handled in
base_rules.mk.

Bug: 9176318
Change-Id: If7460b30ca5da28743487d66da0029a44108d556