Freemium trial notice changes.

Only show trial notice for freemium plans when the trial is active,
and just have the one message: "The %s project is covered by %s's
trial of %d containers. (Add more containers) for parallel builds
 and reduced build queueing once the trial runs out."
More sensible conditional & comment.
Merge pull request #3562 from circleci/freemium-trial-plan-noticies

Freemium trial notice changes.
Merge commit 'f020d2ca8fee07251bbf27a30d742548862c03dd'