apex: drop metadata gathering for multitree.

This was only partially implemented, and is not needed.

Test: presubmits
Change-Id: Ia6534c62051cd484d46333fbbf8a0fa8ce8288e7

apex/Android.bp

@@ -29,7 +29,6 @@ bootstrap_go_package {
         "bp2build.go",
         "deapexer.go",
         "key.go",
-        "metadata.go",
         "prebuilt.go",
         "testing.go",
         "vndk.go",
@@ -39,7 +38,6 @@ bootstrap_go_package {
         "bootclasspath_fragment_test.go",
         "classpath_element_test.go",
         "dexpreopt_bootjars_test.go",
-        "metadata_test.go",
         "platform_bootclasspath_test.go",
         "systemserver_classpath_fragment_test.go",
         "vndk_test.go",