[Ada] Remove repeated setting of Never_Set_In_Source

[Ada] Remove repeated setting of Never_Set_In_Source

Formal parameters have their flag Never_Set_In_Source set at the
beginning of Process_Formals routine (regardless of the parameter mode).
There is no need to set it again when Process_Formals calls
Set_Formal_Mode (for parameters of mode IN OUT and OUT).

Code cleanup related to improved detection of uninitialised objects;
behaviour is unaffected.

gcc/ada/

	* sem_ch6.adb (Set_Formal_Mode): Remove unnecessary setting of
	Never_Set_In_Source.