Add old PERMIT_* forms as poisoned entries in mk.conf.template

I figure it's worth adding the old PERMIT_* forms to the positioned
obsolete entries in /usr/ports/infrastructure/tempalte/mk.conf.template.

OK?

--Kurt

Index: infrastructure/templates/mk.conf.template
===================================================================
RCS file: /cvs/ports/infrastructure/templates/mk.conf.template,v
retrieving revision 1.27
diff -u -p -r1.27 mk.conf.template
--- infrastructure/templates/mk.conf.template 6 Nov 2017 20:43:22 -0000 1.27
+++ infrastructure/templates/mk.conf.template 22 Aug 2019 04:40:24 -0000
@@ -65,3 +65,6 @@
.poison MODGETTEXT_LIB_DEPENDS
.poison MODGETTEXT_RUN_DEPENDS
.poison MODGETTEXT_WANTLIB
+.poison PERMIT_DISTFILES_FTP
+.poison PERMIT_PACKAGE_CDROM
+.poison PERMIT_PACKAGE_FTP