Make registry-facade standard

[csweichel]

We have had registry-facade in our code base for almost a year now, and still it is only a variant. We need to reduce the variance within Gitpod, hence want to move towards a registry-facade only setup.

To this end, we need to:

• remove the registry-facade variance at deploy time
• remove the registry-facade feature flag and all variant code
• remove the static Theia server

Related issues:

• support zero-downtime handover ([registry-facade] Re-deploying Gitpod breaks current image pulls #2512)
• make HTTPS deployment the default in dev-staging ([devstaging] Deploy all branches with HTTPS #2704)
• asses the impact on self-hosted and update the docs accordingly. I'd expect this to possibly make some ingress mode variants obsolete. (Remove support for ingress modes other than hosts #2683)