Simplify soong_java_prebuilt.mk and soong_app_prebuilt.mk

Simplify importing Soong modules into Make by always copying
LOCAL_PREBUILT_MODULE_FILE to LOCAL_BUILT_MODULE, which lets
Soong pick the final output file instead of trying to figure
out which of the various intermediate files should be the
output file.

Also fixes an issue where hostdex modules could attempt to
copy to both $(common_javalib.jar) and $(LOCAL_BUILT_MODULE),
which are the same file for host java modules.

Test: set compile_dex:true on core.platform.api.stubs. no warnings
      of target overriding
Test: m checkbuild

Change-Id: I2e089012436fe8649db82a673d446d1c5a73a731