Don't use enable_github_login option after all

Dependencies

• [2] GNQYRBAG Implement GitHub logins
• [3] 3V374WZK Use email scope
• [4] 3QWDDLBR Add support for logging in via a Google account
• [5] JFW656FT Add a flag to enable Persona support
• [6] 3CH2DFTV Use email api call
• [7] JATZRMWW Lazy load Google and Persona login stuff
• [*] XJRJ4J7M Add user registration
• [*] QL55ECJ6 - adapted ui for hydra, more in line with nixos.org website

Change contents

• edit in src/lib/Hydra/Controller/User.pm at line 161
  [2.197]→[2.197:294](∅→∅)
  − error($c, "Logging in via GitHub is not enabled.") unless $c->config->{enable_github_login};
• edit in src/lib/Hydra/Controller/User.pm at line 207
  [2.1846]→[2.1846:1943](∅→∅)
  − error($c, "Logging in via GitHub is not enabled.") unless $c->config->{enable_github_login};
• replacement in src/root/topbar.tt at line 139
  [2.2334]→[2.2334:2378](∅→∅)
  − [% IF c.config.enable_github_login %]
  [2.2334]

  [2.2378]
  + [% IF c.config.github_client_id %]