ada: Remove Warn_Runtime_Raise attribute from Error_Msg_Object

ada: Remove Warn_Runtime_Raise attribute from Error_Msg_Object

The goal of this attribute is to raise a warning to an error when
the -gnatwE flag is used. This is similar to the existing warnings
as error behavior under the Warn_Err flag so it can be merged.

gcc/ada/ChangeLog:

	* errout.adb: Set Warn_Err as true if Is_Runtime_Error was
	set in the error message.
	* erroutc.adb: Remove instances of Warn_Runtime_Raise.
	* erroutc.ads: Likewise.
	* errutil.adb: Likewise.