ada: Simplify handling of selected components as name references

ada: Simplify handling of selected components as name references

The selector_name of a selected_component always points to an identifier than
is an object name, i.e. specifically, name of a component or discriminant.
There is no need to examine this.

Code cleanup; behavior is unaffected.

gcc/ada/ChangeLog:

	* sem_util.adb (Is_Name_Reference): Remove check for selector_name of a
	selected_component; reuse existing code for indexed components and
	slices.
	(Statically_Names_Object): Remove dead code.