Remove rails erd

The newer version requires some changes to keep pdfs working
I asked the team and no one is using it so remove, we can add it again if we have a need
I did look at the generated output and it did look overly complex - I think a simplified curated diagram might be more useful

Author: zetter-rpf

Gemfile

@@ -73,7 +73,6 @@ group :development, :test do
 end
 
 group :development do
-  gem 'rails-erd'
   gem 'ruby-lsp', require: false
   gem 'ruby-lsp-rspec', '~> 0.1.29', require: false
 end

Gemfile.lock

@@ -137,7 +137,6 @@ GEM
       regexp_parser (>= 1.5, < 3.0)
       xpath (~> 3.2)
     childprocess (4.1.0)
-    choice (0.2.0)
     climate_control (1.2.0)
     coderay (1.1.3)
     concurrent-ruby (1.3.7)
@@ -322,7 +321,6 @@ GEM
       stringio
       time
       uri
-    ostruct (0.6.3)
     paper_trail (17.0.0)
       activerecord (>= 7.1)
       request_store (~> 1.4)
@@ -396,11 +394,6 @@ GEM
       activesupport (>= 5.0.0)
       minitest
       nokogiri (>= 1.6)
-    rails-erd (2.0.2)
-      activerecord (>= 7.0)
-      activesupport (>= 7.0)
-      choice (~> 0.2.0)
-      ostruct
     rails-html-sanitizer (1.7.0)
       loofah (~> 2.25)
       nokogiri (>= 1.15.7, != 1.16.7, != 1.16.6, != 1.16.5, != 1.16.4, != 1.16.3, != 1.16.2, != 1.16.1, != 1.16.0.rc1, != 1.16.0)
@@ -622,7 +615,6 @@ DEPENDENCIES
   rack-cors
   rack_content_type_default (~> 1.1)
   rails (~> 8.1.3)
-  rails-erd
   rails_semantic_logger (~> 4.20)
   rspec
   rspec-rails

README.md

@@ -151,20 +151,6 @@ Handled in `config/initializers/cors.rb`.
 
 This API receives push event data from the [Raspberry Pi Learning](https://github.com/raspberrypilearning) organisation via webhooks. This data is used to create or update code projects related to the [Code Club Projects Site](https://projects.raspberrypi.org), and is processed using the `github_webhooks` gem in the `github_webhooks_controller`. For development purposes, these webhooks are mediated locally through `smee`, which runs in a Docker container.
 
-### Database Structure
-
-Once you have completed the initial setup and have everything running in a container, you can generate an Entity-Relationship Diagram (ERD) to help you to understand the database structure. In order to do this, start things up as usual in one terminal:
-
-`docker-compose up`
-
-then in a second terminal, create the ERD using:
-
-`docker-compose exec api bundle exec erd`
-
-then copy the created ERD out of the container with:
-
-`docker cp "$(docker-compose ps -q api)":/app/EditorAPI-ERD.pdf .`
-
 ## Usage
 
 ### Projects