add description parameter to OPT__DRY_RUN

Allows better help text to be defined than "dry run".  Also make use
of the macro in places that already had a different description.  No
object code changes intended.

Signed-off-by: Rene Scharfe <rene.scharfe@lsrfire.ath.cx>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/notes.c

@@ -804,8 +804,7 @@ static int prune(int argc, const char **argv, const char *prefix)
 	struct notes_tree *t;
 	int show_only = 0, verbose = 0;
 	struct option options[] = {
-		OPT_BOOLEAN('n', "dry-run", &show_only,
-			    "do not remove, show only"),
+		OPT__DRY_RUN(&show_only, "do not remove, show only"),
 		OPT__VERBOSE(&verbose, "report pruned notes"),
 		OPT_END()
 	};