ada: Add tags to warnings controlled by Warn_On_Redundant_Constructs

ada: Add tags to warnings controlled by Warn_On_Redundant_Constructs

Some of the calls to Error_Msg_N controlled by the flag
Warn_On_Redundant_Constructs missed the "?r?" tag in their message
string. This caused a misleading "[enabled by default]" label to appear
next to the error message.

Spotted while adding a warning about duplicated choices in exception
handlers.

gcc/ada/

	* freeze.adb (Freeze_Record_Type): Add tag for redundant pragma Pack.
	* sem_aggr.adb (Resolve_Record_Aggregate): Add tag for redundant OTHERS
	choice.
	* sem_ch8.adb (Use_One_Type): Add tag for redundant USE clauses.