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/apex/apex.go b/apex/apex.go
index 5d0c52a..9ab5187 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -534,7 +534,7 @@
 func (a *apexBundle) getCertString(ctx android.BaseContext) string {
 	certificate, overridden := ctx.DeviceConfig().OverrideCertificateFor(ctx.ModuleName())
 	if overridden {
-		return certificate
+		return ":" + certificate
 	}
 	return String(a.properties.Certificate)
 }