misc/tkcron: Use default tk

tkcron is able to run under any version of tk. Use the default tk
prescribed by the ports tree.

PR:		255624
Reported by:	Chris Hutchinson <portmaster_bsdforge.com
MFH:		2021Q2

misc/tkcron/Makefile

@@ -2,7 +2,7 @@
 
 PORTNAME=	tkcron
 PORTVERSION=	2.12
-PORTREVISION=	2
+PORTREVISION=	3
 CATEGORIES=	misc
 MASTER_SITES=	ftp://ftp.tcl.tk/pub/tcl/mirror/ftp.procplace.com/sorted/packages-7.6/misc/tkcron-2.12/ \
 		http://ftp.sunet.se/pub/lang/tcl/sorted/packages-7.6/misc/tkcron-2.12/ \
@@ -14,7 +14,7 @@ EXTRACT_SUFX=	.tcl.gz
 MAINTAINER=	cy@FreeBSD.org
 COMMENT=	Frontend to crontab
 
-USES=		tk:85,run
+USES=		tk:,run
 
 EXTRACT_CMD=	${GZIP_CMD}
 EXTRACT_BEFORE_ARGS= -cd