android_app_import is now ApexModule

Like other prebuilts (java_import, etc.), android_app_import has now
became ApexModule. It means it supports APEX-specific properties like
apex_available, min_sdk_version, etc.

Bug: 154488897
Test: m
Change-Id: I86f02771496ffc68c98a50ddfc786788fa1e05fb
diff --git a/java/androidmk.go b/java/androidmk.go
index 7d57525..68da23e 100644
--- a/java/androidmk.go
+++ b/java/androidmk.go
@@ -626,6 +626,11 @@
 }
 
 func (a *AndroidAppImport) AndroidMkEntries() []android.AndroidMkEntries {
+	if !a.IsForPlatform() {
+		// The non-platform variant is placed inside APEX. No reason to
+		// make it available to Make.
+		return nil
+	}
 	return []android.AndroidMkEntries{android.AndroidMkEntries{
 		Class:      "APPS",
 		OutputFile: android.OptionalPathForPath(a.outputFile),