Fixes a bug that results in a broken opensearch.xml for team subdomains.
See https://github.com/outline/outline/issues/3470 -- this issue (same reproduction steps) is happening again due to an issue introduced in 3eabb30949 .
The team subdomain's `/opensearch.xml` is correct, but because the `<link rel="search" ...` points to the CDN, this correct opensearch.xml is not used.