Mixed builds is supported for all apex module types, not just "apex".

This includes apex_test and apex_vndk. Rely on mixed builds module
allowlist to filter further.

Test: presubmits
Test: m test_com.android.adbd; showcommands test_com.android.adbd | tail -n1 | grep bazel-out
Change-Id: Id73db0917ad4a6dd9c0646d5186753ed940e735f
diff --git a/apex/apex.go b/apex/apex.go
index 4424b22..6df9651 100644
--- a/apex/apex.go
+++ b/apex/apex.go
@@ -1939,7 +1939,7 @@
 var _ android.MixedBuildBuildable = (*apexBundle)(nil)
 
 func (a *apexBundle) IsMixedBuildSupported(ctx android.BaseModuleContext) bool {
-	return ctx.ModuleType() == "apex" && a.properties.ApexType == imageApex
+	return a.properties.ApexType == imageApex
 }
 
 func (a *apexBundle) QueueBazelCall(ctx android.BaseModuleContext) {