Fix wrong construct_array_builtin() call in GUCArrayDelete()

The current code unintentionally uses the wrong datum to construct an array.
The bug was introduced by 096dd80f3c, so no backpatching is needed.

Reported-by: David Steele
Discussion: https://postgr.es/m/d46f9265-ff3c-6743-2278-6772598233c2%40pgmasters.net
Author: Nathan Bossart
Reviewed-by: David Steele, Tom Lane

src/backend/utils/misc/guc.c

@@ -6496,7 +6496,8 @@ GUCArrayDelete(ArrayType *array, ArrayType **usersetArray, const char *name)
 		{
 			newarray = construct_array_builtin(&d, 1, TEXTOID);
 			if (usersetArray)
-				newUsersetArray = construct_array_builtin(&d, 1, BOOLOID);
+				newUsersetArray = construct_array_builtin(&userSetDatum, 1,
+														  BOOLOID);
 		}
 
 		index++;