dex_import that isn't available for platform isn't installed

This change fixes a bug that dex_import module is always installed to
the platform even when the module is not available to the platform.

Bug: 158284983
Test: OUT_DIR=/tmp/ndk build/soong/scripts/build-ndk-prebuilts.sh
Change-Id: I85570506e700be59ee63e4f1d7902a40e36df39c

java/java.go

@@ -2741,8 +2741,10 @@ func (j *DexImport) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 
 	j.maybeStrippedDexJarFile = dexOutputFile
 
+	if j.IsForPlatform() {
 		ctx.InstallFile(android.PathForModuleInstall(ctx, "framework"),
 			j.Stem()+".jar", dexOutputFile)
+	}
 }
 
 func (j *DexImport) DexJar() android.Path {