hooks: Remove deprecated hooks dir

Over a year ago, through e0824f17, the
hooks in this repository were updated to not be successful, basically
block each push from happening.

This change removes the hooks, and updates the documentation. There's no
customer impact, and these changes are just part of a general cleanup.

README.md

@@ -18,25 +18,6 @@ An overview of the four cases described above:
 1. git pull over SSH -> gitlab-shell -> API call to gitlab-rails (Authorization) -> accept or decline -> establish Gitaly session
 1. git push over SSH -> gitlab-shell (git command is not executed yet) -> establish Gitaly session -> (in Gitaly) gitlab-shell pre-receive hook -> API call to gitlab-rails (authorization) -> accept or decline push
 
-## Git hooks
-
-The gitlab-shell repository used to also contain the
-Git hooks that allow GitLab to validate Git pushes (e.g. "is this user
-allowed to push to this protected branch"). These hooks also trigger
-events in GitLab (e.g. to start a CI pipeline after a push).
-
-We are in the process of moving these hooks to Gitaly, because Git hooks
-require direct disk access to Git repositories, and that is only
-possible on Gitaly servers. It makes no sense to have to install
-gitlab-shell on Gitaly servers.
-
-As of GitLab 11.10  [the actual Git hooks are in the Gitaly
-repository](https://gitlab.com/gitlab-org/gitaly/tree/v1.22.0/ruby/vendor/gitlab-shell/hooks),
-but gitlab-shell must still be installed on Gitaly servers because the
-hooks rely on configuration data (e.g. the GitLab internal API URL) that
-is not yet available in Gitaly itself. Also see the [transition
-plan](https://gitlab.com/gitlab-org/gitaly/issues/1226#note_126519133).
-
 ## Code status
 
 [![pipeline status](https://gitlab.com/gitlab-org/gitlab-shell/badges/master/pipeline.svg)](https://gitlab.com/gitlab-org/gitlab-shell/-/pipelines?ref=master)

hooks/post-receive

-#!/bin/sh
-echo "The gitlab-shell hooks have been migrated to Gitaly, see https://gitlab.com/gitlab-org/gitaly/issues/1226"
-exit 1
-

hooks/pre-receive

-#!/bin/sh
-echo "The gitlab-shell hooks have been migrated to Gitaly, see https://gitlab.com/gitlab-org/gitaly/issues/1226"
-exit 1
-

hooks/update

-#!/bin/sh
-echo "The gitlab-shell hooks have been migrated to Gitaly, see https://gitlab.com/gitlab-org/gitaly/issues/1226"
-exit 1
-