[Ada] Do not use front-end build-in-place mechanism for nonlimited types

[Ada] Do not use front-end build-in-place mechanism for nonlimited types

It was only used in specific cases for controlled types but no longer
provides any significant benefit in practice.

gcc/ada/

	* debug.adb (d.9): Remove usage.
	* exp_ch6.adb (Expand_Simple_Function_Return): Remove redundant
	test on Debug_Flag_Dot_L.
	(Is_Build_In_Place_Result_Type): Return false for nonlimited types.
	(Is_Build_In_Place_Function): Tidy up and remove redundant test on
	Debug_Flag_Dot_L.