The parent was Node_Kind before. This is a minor cleanup, and has no
effect on the operation of the compiler.  However, if we start declaring
more objects of the various predicated subtypes, such as
N_Declaration_Id, it would be good to get them right.

Tested on x86_64-pc-linux-gnu, committed on trunk

gcc/ada/

	* gen_il-gen-gen_nodes.adb: Change the parent of
	N_Exception_Declaration to be N_Declaration.  Minor comment fix.