fix: duplicate migration files in Dockerfile

[froger]

The original image git.octree.ch:4567/decidim/vocacity/system/decidim-0.27 have already migrations files in it. With this PR, we remove the migration from this first image, and replace them with the one present in our mautic repository.

This will fix the following error on development redeploy, while doing a rails db:migrate:

rails aborted!
ActiveRecord::DuplicateMigrationNameError:

Multiple migrations have the name DeviseCreateDecidimUsers.

Tasks: TOP => db:migrate