API doc: make footer link font colors be uniform
API doc: make footer link font colors be uniform

Both visited and non-visited link will now have the same color, avoiding
gray-on-black low contrast effects.

This partially reverts commit 8b283648aa4c0dc0ceae9d5a496432a1e8550be5.

SoftwareHeritage/swh-web-ui,SoftwareHeritage/swh-web-ui,SoftwareHeritage/swh-web-ui