pgsql: Remove psql's ancient hack that suppressed functions taking or

Log Message:
-----------
Remove psql's ancient hack that suppressed functions taking or returning
cstring from the output of \df. Now that the default behavior is to
exclude all system functions, the de-cluttering rationale for this behavior
seems pretty weak; and it was always quite confusing/unhelpful if you were
actually looking for I/O functions. (Not to mention if you were looking
for encoding converters or other cases that might take or return cstring.)

Modified Files:
--------------
pgsql/doc/src/sgml/ref:
psql-ref.sgml (r1.222 -> r1.223)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/ref/psql-ref.sgml?r1=1.222&r2=1.223)
pgsql/src/bin/psql:
describe.c (r1.207 -> r1.208)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/bin/psql/describe.c?r1=1.207&r2=1.208)