Remove infrastructure/docker cruft

[ocket8888]

This tech debt affects these Traffic Control components:

none

Current behavior:

There are a bunch of Dockerfiles sitting under infrastructure/docker/ (not counting the ones in infrastructure/docker/build that are used by pkg) that have no current possible use and should be removed to avoid having e.g. usages old API versions in the codebase that nobody wants to fix because nobody actually uses those. The Dockerfiles in question were meant to represent a minimal ATC system for use in development and testing. I arrogantly assert that CDN-in-a-Box at infrastructure/cdn-in-a-box and the developer environment at dev/ have rendered these Dockerfiles obsolete.

According to the CHANGELOG, Traffic Ops API version 1.x was removed on 2021-08-30. Those Dockerfiles use API version 1.2 (until #6869 is merged). That means that for roughly 8 months those Docker images that relied on it in infrastructure/docker/ have been broken. They are currently broken in latest supported release of ATC, which evidently nobody thought was worth a -1.

So it appears truly nobody has been using these for quite some time.

New behavior:

Get rid of 'em.