Clean up LOCAL_DONT_DELETE_JAR_META_INF

Allow setting it for host modules, it is necessary for
RoboLectric.

Remove some unused PRIVATE_DONT_DELETE_JAR_META_INF variables.

Remove unzip-jar-files, it is obsolete since merge_zips was
introduced.

Test: m checkbuild
Change-Id: I3f2fc466321904eace31525cbac99ad524f39188
diff --git a/core/host_java_library.mk b/core/host_java_library.mk
index c8d2ee7..f7bf337 100644
--- a/core/host_java_library.mk
+++ b/core/host_java_library.mk
@@ -95,13 +95,15 @@
 javac-check-$(LOCAL_MODULE) : $(full_classes_compiled_jar)
 .PHONY: javac-check-$(LOCAL_MODULE)
 
+$(full_classes_combined_jar): PRIVATE_DONT_DELETE_JAR_META_INF := $(LOCAL_DONT_DELETE_JAR_META_INF)
 $(full_classes_combined_jar): $(full_classes_compiled_jar) \
                               $(jar_manifest_file) \
                               $(full_static_java_libs) | $(MERGE_ZIPS)
 	$(if $(PRIVATE_JAR_MANIFEST), $(hide) sed -e "s/%BUILD_NUMBER%/$(BUILD_NUMBER_FROM_FILE)/" \
             $(PRIVATE_JAR_MANIFEST) > $(dir $@)/manifest.mf)
 	$(MERGE_ZIPS) -j --ignore-duplicates $(if $(PRIVATE_JAR_MANIFEST),-m $(dir $@)/manifest.mf) \
-            -stripDir META-INF -zipToNotStrip $< $@ $< $(call reverse-list,$(PRIVATE_STATIC_JAVA_LIBRARIES))
+            $(if $(PRIVATE_DONT_DELETE_JAR_META_INF),,-stripDir META-INF -zipToNotStrip $<) \
+            $@ $< $(call reverse-list,$(PRIVATE_STATIC_JAVA_LIBRARIES))
 
 # Run jarjar if necessary, otherwise just copy the file.
 ifneq ($(strip $(LOCAL_JARJAR_RULES)),)