Revert "Merge branch 'fc/transport-helper-sync-error-fix'"

This reverts commit d508e4a8e2391ae2596403b6478d01cf3d5f928f,
reversing changes made to e42552135a2a396f37053a89f44952ea907870b2.

The author of the original topic says he broke the upcoming 2.0
release with something that relates to "synchronization crash
regression" while refusing to give further specifics, so this would
unfortunately be the safest option for the upcoming release.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
contrib: remote-helpers: add move warnings (v2.0)

The tools are now maintained out-of-tree, and they have a regression
in v2.0. It's better to start warning the users as soon as possible.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
remote-helpers: point at their upstream repositories

Signed-off-by: Junio C Hamano <gitster@pobox.com>
remote-helpers: give short instructions to download the latest

Signed-off-by: Junio C Hamano <gitster@pobox.com>