php-fpm: change FPM_USER/FPM_GROUP

pkgsrc changes:
---------------
  * Remove CATEGORIES since it is already included by ${PHPPKGSRCDIR}/Makefile.common.
  * Following a discussion on teck-pkg@ (https://mail-index.netbsd.org/tech-pkg/2020/04/07/msg022973.html)
    it seems preferable to dissociate the php-fpm user from the one of the Apache web
    server for at least two reasons: (i) www/apache is no longer necessarily the
    standard approach and (ii) running a daemon with a dedicated user seems to be more
    in line with best practices.

www/php-fpm/Makefile

@@ -1,8 +1,7 @@
-# $NetBSD: Makefile,v 1.29 2020/01/18 21:51:10 jperkin Exp $
+# $NetBSD: Makefile,v 1.30 2020/04/15 11:57:35 triaxx Exp $
 
 PKGNAME=	${PHP_PKG_PREFIX}-fpm-${PHP_VERSION}
 PKGREVISION=	3
-CATEGORIES=	www
 
 HOMEPAGE=	https://php-fpm.org/
 MAINTAINER=	[email protected]
@@ -16,8 +15,8 @@ LIBTOOL_OVERRIDE=	# empty
 
 .include "../../mk/bsd.prefs.mk"
 
-FPM_USER?=		${APACHE_USER}
-FPM_GROUP?=		${APACHE_GROUP}
+FPM_USER?=		fpm
+FPM_GROUP?=		www
 
 BUILD_DEFS+=		VARBASE FPM_USER FPM_GROUP