Remove fallback to classes jars from bootclasspath_fragment

Previously, the hidden API processing performed by the
platform_bootclasspath would try and get flag files from the fragments
it references but would fall back to the classes jars. This change
removes that logic as it is no longer needed as all fragments, both
source and prebuilts, provide flag files and the prebuilts no longer
provide valid classes jars.

Bug: 194063708
Test: m out/soong/hiddenapi/hiddenapi-flags.csv
      - check that this does not change the contents.
Change-Id: Ib867a08508f5a0f8858f6baedebbe99b6a825f80

java/hiddenapi_monolithic.go

@@ -58,30 +58,20 @@ func newMonolithicHiddenAPIInfo(ctx android.ModuleContext, flagFilesByCategory F
 	// Merge all the information from the classpathElements. The fragments form a DAG so it is possible that
 	// this will introduce duplicates so they will be resolved after processing all the classpathElements.
 	for _, element := range classpathElements {
-		var classesJars android.Paths
 		switch e := element.(type) {
 		case *ClasspathLibraryElement:
-			classesJars = retrieveClassesJarsFromModule(e.Module())
+			classesJars := retrieveClassesJarsFromModule(e.Module())
+			monolithicInfo.ClassesJars = append(monolithicInfo.ClassesJars, classesJars...)
 
 		case *ClasspathFragmentElement:
 			fragment := e.Module()
 			if ctx.OtherModuleHasProvider(fragment, HiddenAPIInfoProvider) {
 				info := ctx.OtherModuleProvider(fragment, HiddenAPIInfoProvider).(HiddenAPIInfo)
 				monolithicInfo.append(&info)
-
-				// If the bootclasspath fragment actually perform hidden API processing itself then use the
-				// CSV files it provides and do not bother processing the classesJars files. This ensures
-				// consistent behavior between source and prebuilt as prebuilt modules do not provide
-				// classesJars.
-				if info.AllFlagsPath != nil {
-					continue
-				}
+			} else {
+				ctx.ModuleErrorf("%s does not provide hidden API information", fragment)
 			}
-
-			classesJars = extractClassesJarsFromModules(e.Contents)
 		}
-
-		monolithicInfo.ClassesJars = append(monolithicInfo.ClassesJars, classesJars...)
 	}
 
 	// Dedup paths.