[ticket/12830] Remove double .postlink in colours.css

PHPBB3-12830
Merge pull request #2710 from Crizz0/ticket/12830

[ticket/12830] Removes double .postlink in colours.css

* Crizz0/ticket/12830:
  [ticket/12830] Remove double .postlink in colours.css
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/12830] Remove double .postlink in colours.css