Removing unnecessary code from JModelAdmin

I stumbled over this one during a code review. If this introduces any change, then we have bigger problems...

We are first checking if $this->type equals false. If that is the case, we create a new JUcmType object and get the type by alias. Then we do the same again, except that we assign the typeAlias. If $this->type does not equal false, we again assign the typeAlias. Long story short, double the code, always assigning $typeAlias => we can remove that part.