Refactor special handling of hidden API encoding for master-art

Instead of encoding the hidden API with an empty set of flags when the
monolithic flags are not available this simply disables encoding
altogether which should have the same behavior at runtime.

This change also removes the unused flags field in hiddenAPISingleton
which was set but never read.

Bug: 179354495
Test: m nothing
Change-Id: I32d5825e5271829993dd4e5be4d4ee1b22fa7b22

java/hiddenapi.go

@@ -92,6 +92,12 @@ func (h *hiddenAPI) initHiddenAPI(ctx android.BaseModuleContext, configurationNa
 
 	h.configurationName = configurationName
 
+	// If the frameworks/base directories does not exist and no prebuilt hidden API flag files have
+	// been configured then it is not possible to do hidden API encoding.
+	if !ctx.Config().FrameworksBaseDirExists(ctx) && ctx.Config().PrebuiltHiddenApiDir(ctx) == "" {
+		return
+	}
+
 	// It is important that hiddenapi information is only gathered for/from modules that are actually
 	// on the boot jars list because the runtime only enforces access to the hidden API for the
 	// bootclassloader. If information is gathered for modules not on the list then that will cause
@@ -303,11 +309,7 @@ func hiddenAPIEncodeDex(ctx android.ModuleContext, output android.WritablePath,
 	}
 
 	enforceHiddenApiFlagsToAllMembers := true
-	// If frameworks/base doesn't exist we must be building with the 'master-art' manifest.
-	// Disable assertion that all methods/fields have hidden API flags assigned.
-	if !ctx.Config().FrameworksBaseDirExists(ctx) {
-		enforceHiddenApiFlagsToAllMembers = false
-	}
+
 	// b/149353192: when a module is instrumented, jacoco adds synthetic members
 	// $jacocoData and $jacocoInit. Since they don't exist when building the hidden API flags,
 	// don't complain when we don't find hidden API flags for the synthetic members.