Revert "Add override_module."

This reverts commit aa65e17016152d0d73cd10ab3987bc3bd5c2ef91.

Reason for revert: Not compatible with PRODUCT_PACKAGES, and so has very limited use.

Change-Id: Ib141d3984a6f12bb50989e66037494c466b066f1
diff --git a/java/app.go b/java/app.go
index 08b2d91..c08aefd 100644
--- a/java/app.go
+++ b/java/app.go
@@ -392,7 +392,7 @@
 func (a *AndroidApp) getCertString(ctx android.BaseContext) string {
 	certificate, overridden := ctx.DeviceConfig().OverrideCertificateFor(ctx.ModuleName())
 	if overridden {
-		return certificate
+		return ":" + certificate
 	}
 	return String(a.appProperties.Certificate)
 }