refactor: import of CtRole

[surli]

This PR is related to #2100

We used a lot this of construction in our code:

import CtRole;
import static CtRole.AROLE;

@myRole(role = CtRole.AROLE);
public void method() {
  aCall(AROLE);
}

This is perfectly correct code, but it's a kind of redundancy to import twice CtRole where we used only the static field already imported.
Moreover the import mechanism will align all this behaviour to only one import, which is the static one.
Then as we got now one test to check that Spoon imports and computed imports are the same, I propose to refactor to only use the import of the static field.