feeds: management: remove dead and out of project feed

Remove management feed which has not been active since some years.

Signed-off-by: Sven Roederer <devel-sven@geroedel.de>

feeds.conf.default

@@ -4,6 +4,5 @@ src-git routing https://git.openwrt.org/feed/routing.git
 src-git telephony https://git.openwrt.org/feed/telephony.git
 #src-git video https://github.com/openwrt/video.git
 #src-git targets https://github.com/openwrt/targets.git
-#src-git management https://github.com/openwrt-management/packages.git
 #src-git oldpackages http://git.openwrt.org/packages.git
 #src-link custom /usr/src/openwrt/custom-feed