Don't install android_library modules

Skip dexing and installing android_library modules, the platform
can't load them directly anyways.

Test: m checkbuild
Change-Id: I4940569f0deb0eefbe52ac1bee6a32a8b2a2c5be
diff --git a/java/aar.go b/java/aar.go
index 506f39f..e054d24 100644
--- a/java/aar.go
+++ b/java/aar.go
@@ -323,6 +323,7 @@
 		&module.androidLibraryProperties)
 
 	module.androidLibraryProperties.BuildAAR = true
+	module.properties.Installable = proptools.BoolPtr(false)
 
 	android.InitAndroidArchModule(module, android.DeviceSupported, android.MultilibCommon)
 	return module