Remove Omnibus project from early-merging phase

What does this MR do?

Remove Omnibus project from early-merging phase

While implementing pipelines for merged results, it was assumed Omnibus were using the same CI rules, but apparently, it needs some specific CI variables. See https://sentry.gitlab.net/gitlab/release-tools/issues/1878821/?referrer=slack

This commit removes Omnibus from early-merge phase until further investigation is done