Use merge_zips to merge jars during Java build in Make.

1. Use merge_zips to merge jars without unzipping/rezipping static Java
libraries. And seperate merging process as a independent Make target so
that Javac can only depend on Turbine.

2. Remove duplicate vars: "full_java_lib_deps" in droiddoc.mk

3. Also use classes-header.jar for link_apk & link_instr

Bug: b/65455145
Test: m clean && m -j32

Change-Id: I7b0307664a6b86075c983284fce099bd3946318c