Remove macOS in a favor of a link to the platform repo's releases

Thank you @claudiodekker for providing signed releases here, I assume with https://github.com/ungoogled-software/ungoogled-chromium-macos/pull/195 merged there's no functional difference between whats getting published here and the releases from the platform repository. I'd like to remove the builds in favor of a link there. What do you think? CC @Cubik65536 See also https://github.com/ungoogled-software/ungoogled-chromium-macos/issues/179