ada: Remove redundant parentheses inside unary operators (cont.)

GNAT already emits a style warning when redundant parentheses appear inside
logical and short-circuit operators. A similar warning will be soon emitted for
unary operators as well. This patch removes the redundant parentheses to avoid
build errors.

gcc/ada/ChangeLog:

	* libgnat/a-strunb.ads: Remove redundant parentheses inside NOT
	operators.