rc: remove old captive portal rrd files on bootup

src/etc/rc

@@ -222,6 +222,10 @@ fi
 # Execute the normal syshook / plugin commands
 /usr/local/etc/rc.syshook start
 
+# 16.1 migration code for stale captive portal files to be removed in 16.7
+rm -rf /var/db/rrd/*-concurrent.rrd
+rm -rf /var/db/rrd/*-loggedin.rrd
+
 echo -n "Starting CRON... "
 cd /tmp && /usr/sbin/cron -s 2>/dev/null
 echo "done."