ada: Remove unreachable code in Resolve_Extension_Aggregate

The only functions using the BIP protocol are now those returning a limited
type: Is_Build_In_Place_Result_Type => Is_Inherently_Limited_Type.

gcc/ada/

	* sem_aggr.adb (Resolve_Extension_Aggregate): Remove the unreachable
	call to Transform_BIP_Assignment as well as the procedure.