Hide 'Support metric: X%' on campaign pages

[CooperSmout]

Currently each campaign page (e.g. https://www.freeourknowledge.org/campaign/support-fee-free-open-access-journals) lists a second support metric (after Total pledges) called 'Support metric: TBD%', because the flagship OA campaigns were designed to activate using a percentage-based measure of impact rather than number of pledges. The new campaigns we're developing will only use Total pledges to activate, and so we need to hide the 'Support metric' for these new campaigns. In the future this could be done by making the support metric optional for each campaign, but to keep things simple for now (and quick turnaround) we can just hide the 'Support metric' and add it back in later on a per-campaign basis if needed for the flagship OA campaigns.