x11-themes/gnome-icon-theme-symbolic: fix build

After the removal of gtk-update-icon-cache, this port wrongly was
calling it at build time.
Ensure it is not needed anymore.
While here:
  remove unneeded USE_GNOME=gnomeprefix and USES=gnome
  add license

Reported by:	antoine

x11-themes/gnome-icon-theme-symbolic/Makefile

@@ -10,18 +10,15 @@ DIST_SUBDIR=	gnome3
 MAINTAINER=	gnome@FreeBSD.org
 COMMENT=	GNOME Symbolic Icons
 
+LICENSE=	CC-BY-SA-3.0
+LICENSE_FILES=	${WRKSRC}/COPYING
+
 BUILD_DEPENDS=	icon-naming-utils>=0.8.7:x11-themes/icon-naming-utils
 
-USES=		gmake gnome pathfix pkgconfig tar:xz
-USE_GNOME=	gnomeprefix
+USES=		gmake localbase pathfix pkgconfig tar:xz
 GNU_CONFIGURE=	yes
 CONFIGURE_ENV=	ac_cv_path_GIT="" \
-		ac_cv_path_INKSCAPE=""
-CPPFLAGS+=	-I${LOCALBASE}/include
-LDFLAGS+=	-L${LOCALBASE}/lib
-
-post-patch:
-	@${REINPLACE_CMD} -e 's|(GTK_UPDATE_ICON_CACHE) -q |(GTK_UPDATE_ICON_CACHE) -q -t -f |'g \
-		${WRKSRC}/Makefile.in
+		ac_cv_path_INKSCAPE="" \
+		ac_cv_path_GTK_UPDATE_ICON_CACHE=/usr/bin/true
 
 .include <bsd.port.mk>