Stop symlinking hooks on repository creation

In an earlier MR1 hooks are executed not through the symlink, but leveraging the -c flag on the git binary. This works well, but when #run_git was executed in Gitaly-Ruby the hooks weren't executed the new way.

Luckily this was covered by tests, and the symlinking strategy remained employed. This commit fixes the bug where the hooks weren't executed and now allows the removal of the code that set the hooks.

Part of: #1226 (closed)

Closes: #1392 (closed)