This reverts commit e385e467.

While this option was undocumented it exists to make possible to pass
parameters to the route helpers that are reserved like `:domain`.

While `url_for(domain: 'foo.com')` would generate a URL in the `foo.com`
domain `url_for(params: { domain: 'foo.com' })` would generate a URL
with `?domain=foo.com`.