Remove fake repository_path response

Regarding:

# From lib/api/internal.rb
# Return value for `/allowed`
{                                                                                                                                                                                                                                                                       
  status: true,
  gl_repository: gl_repository,
  gl_id: Gitlab::GlId.gl_id(user),
  gl_username: user&.username,                                                                                                                                                                                                                                          
  
  # This repository_path is a bogus value but gitlab-shell still requires                                                                                                                                                                                               
  # its presence. https://gitlab.com/gitlab-org/gitlab-shell/issues/135                                                                                                                                                                                                 
  repository_path: '/',                                                                                                                                                                                                                                                 
  
  gitaly: gitaly_payload(params[:action])                                                                                                                                                                                                                               
}

After 8fad0738 got merged, the root path was always returned to Gitlab-shell, as it wanted to do some additional checks. These checks can be removed after gitlab-shell!231 (merged) is merged and released.

cc @rspeicher @nick.thomas