Replace jniDependencyTag with a value

Support GetDirectDepsWithTag on JNI deps by replacing the
jniDependencyTag type with a jniLibTag value.

Test: app_test.go
Change-Id: I8d66a5d3f433562e131a1fbafce75891d1b094dd
diff --git a/java/app.go b/java/app.go
index c25835c..76b3598 100755
--- a/java/app.go
+++ b/java/app.go
@@ -379,7 +379,6 @@
 			"can only be set for modules that set sdk_version")
 	}
 
-	tag := &jniDependencyTag{}
 	for _, jniTarget := range ctx.MultiTargets() {
 		variation := append(jniTarget.Variations(),
 			blueprint.Variation{Mutator: "link", Variation: "shared"})
@@ -393,7 +392,7 @@
 			Bool(a.appProperties.Jni_uses_sdk_apis) {
 			variation = append(variation, blueprint.Variation{Mutator: "sdk", Variation: "sdk"})
 		}
-		ctx.AddFarVariationDependencies(variation, tag, a.appProperties.Jni_libs...)
+		ctx.AddFarVariationDependencies(variation, jniLibTag, a.appProperties.Jni_libs...)
 	}
 
 	a.usesLibrary.deps(ctx, sdkDep.hasFrameworkLibs())