[Greenwich] Update link colour.

[dracos]

Update to match their site. The front page colour didn't seem to do anything, and the visited seemed pointless. [skip changelog] Fixes https://github.com/mysociety/societyworks/issues/3435

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.49%. Comparing base (caae438) to head (73acd35).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5180      +/-   ##
==========================================
- Coverage   82.49%   82.49%   -0.01%     
==========================================
  Files         406      406              
  Lines       31716    31716              
  Branches     5044     5044              
==========================================
- Hits        26164    26163       -1     
- Misses       4063     4064       +1     
  Partials     1489     1489              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[lucascumsille]

The other approach would be to remove the visited bit altogether.

[lucascumsille]

@dracos I think this should be ready =)