Chore: Remove Redis for Rack Attack (#4873)

Because:
- It is no longer required

app.json

@@ -12,12 +12,7 @@
         { "url": "https://github.com/devforce/heroku-buildpack-cleanup" }
       ],
       "addons": [
-        "heroku-postgresql:mini",
-        "heroku-redis:mini",
-        {
-          "plan": "heroku-redis:minis",
-          "as": "REDIS_FOR_RACK_ATTACK"
-        }
+        "heroku-postgresql:mini"
       ],
       "env": {
         "STAGING": {

config/initializers/rack_attack.rb

@@ -1,6 +1,4 @@
 class Rack::Attack
-  Rack::Attack.enabled = ENV['ENABLE_RACK_ATTACK'] || Rails.env.production?
-
   # Rack::Attack.cache.store = Redis.new(url: ENV['REDIS_FOR_RACK_ATTACK_URL']) if ENV['REDIS_FOR_RACK_ATTACK_URL']
 
   ### Throttle Spammy Clients ###

env.sample

@@ -12,5 +12,3 @@ GITHUB_SECRET: 1234
 GITHUB_WEBHOOK_SECRET: 1234
 GOOGLE_CLIENT_ID: 1234
 GOOGLE_CLIENT_SECRET: 1234
-
-ENABLE_RACK_ATTACK: 'true'