[Ada] Remove repeated description of support for Address clauses

[Ada] Remove repeated description of support for Address clauses

The GNAT behaviour regarding the Ada RM requirement to support Address
clauses for imported subprograms was documented twice: in section about
packed types (which was a mistake) and in section about address clauses
(where it belongs).

Cleanup related to the use of packed arrays for bitset operations to
detect uses of uninitialized scalars in GNAT.

gcc/ada/

	* doc/gnat_rm/implementation_advice.rst (Packed Types): Remove
	duplicated and wrongly placed paragraph.
	* gnat_rm.texi: Regenerate.