Remove DEFAULT_REMOTE constant

Closes https://gitlab.com/gitlab-org/release-tools/issues/288

0b542025 - Update RuboCop rules

We like ordered gems; AlignHash is a little too nit-picky.

9a71d42a - Move AutoDeploy::Version spec to correct location

f571e8c9 - Rename gitlab remote to canonical

This better describes which remote is the "source of truth", because not all projects using gitlab were actually on gitlab.com.

f1f0bb29 - Prevent stubbed feature flags from cross-polluting

227bed71 - Remove the DEFAULT_REMOTE constant

The last use of this was in a1620ff4, and we now have the canonical name to better describe what the remote is intended for.