remove direct reference to <R_ext/RS.h>

Author: Tomoaki Nishiyama

RPostgreSQL/DESCRIPTION

@@ -1,6 +1,6 @@
 Package: RPostgreSQL
 Version: 0.7-1
-Date: 2021-08-03
+Date: 2021-09-09
 Title: R Interface to the 'PostgreSQL' Database System
 Author: Joe Conway, Dirk Eddelbuettel, Tomoaki Nishiyama, Sameer Kumar Prayaga (during 2008), Neil Tiffin
 Maintainer: Tomoaki Nishiyama <tomoakin@staff.kanazawa-u.ac.jp>

RPostgreSQL/src/RS-pgsql-copy.c

@@ -6,7 +6,7 @@
 
 #include "RS-PostgreSQL.h"
 #include <Rinternals.h>  
-#include <R_ext/RS.h>  /* for Calloc/Free */
+#include <R.h>  /* for Calloc/Free */
 #include <ctype.h>
 #include <stdlib.h>
 #include <errno.h>