chore: remove references to dbtestutil.WillUsePostgres (#20436)

Addresses https://github.com/coder/internal/issues/758.

This PR only cleans up dead code, it makes no changes to test logic.

coderd/workspacestats/tracker_test.go

@@ -110,9 +110,6 @@ func TestTracker(t *testing.T) {
 // This test performs a more 'integration-style' test with multiple instances.
 func TestTracker_MultipleInstances(t *testing.T) {
 	t.Parallel()
-	if !dbtestutil.WillUsePostgres() {
-		t.Skip("this test only makes sense with postgres")
-	}
 
 	// Given we have two coderd instances connected to the same database
 	var (