Also remove the msg.mk files used for old apicheck.
And export jdiff-doc.zip generated by Soong.
Test: api-stubs-docs-diff
Bug: b/78245848
Change-Id: I329aa375623a7b7a121d58314dab694a326c9f0f
Soong droiddoc modules were using soong_java_prebuilt.mk, but they
don't need any of the java logic from it, and it includes
base_rules.mk which was not included by droiddoc.mk. Add
soong_droiddoc_prebuilt.mk that just installs the droiddoc
outputs without including base_rules.mk.
Fixes building docs modules in mm, mma, and m checkbuild.
Bug: 112388925
Test: m docs
Change-Id: I4f7262e2c3b1afbee44c1cc306330885b687a074