Stop prebuilt_apex/apex_set exporting invalid jars to Make

A prebuilt_apex/apex_set module can make a dex implementation jar
available for use by Make targets but it does not have access to a real
classes implementation jar; the jar in the corresponding sdk is just an
empty file. Exporting that invalid file to Make means that the phony
target created for the module depends on an invalid classes jar which
causes the build to fail.

This change removes the logic that make classes and header jars
available to Make so that building the phony target no longer fails.

Bug: 202521005
Test: m TARGET_PRODUCT=armv8 TARGET_PRODUCT_VARIANT=eng TARGET_BUILD_UNBUNDLED=true SOONG_ALLOW_MISSING_DEPENDENCIES=true core-icu4j
      - above was performed in master-art.
Change-Id: If667b36b988e2d331acd85f60f3369778838d034