Merge branch 'jl/remote-rm-prune'

"git remote rm" and "git remote prune" can involve removing many
refs at once, which is not a very efficient thing to do when very
many refs exist in the packed-refs file.

* jl/remote-rm-prune:
remote prune: optimize "dangling symref" check/warning
remote: repack packed-refs once when deleting multiple refs
remote rm: delete remote configuration as the last

diff --cc builtin/remote.c
Simple merge

diff --cc refs.c
Simple merge

diff --cc refs.h
Simple merge