DEV: Remove db_timeout setting (#22912)

It doesn't actually do anything.

app/models/global_setting.rb

@@ -125,7 +125,6 @@ class GlobalSetting
     %w[
       pool
       connect_timeout
-      timeout
       socket
       host
       backup_host

config/database.yml

@@ -4,7 +4,6 @@ development:
   database: <%= ENV['DISCOURSE_DEV_DB'] || 'discourse_development' %>
   min_messages: warning
   pool: 5
-  timeout: 5000
   checkout_timeout: <%= ENV['CHECKOUT_TIMEOUT'] || 5 %>
   host_names:
     ### Don't include the port number here. Change the "port" site setting instead, at /admin/site_settings.
@@ -38,7 +37,6 @@ test:
   database: <%= test_db %>
   min_messages: warning
   pool: 5
-  timeout: 5000
   host_names:
     - test.localhost
 
@@ -49,7 +47,6 @@ profile:
   database: discourse_profile
   min_messages: warning
   pool: 5
-  timeout: 5000
   host_names:
     - "localhost"
 # You may be surprised production is not here, it is sourced from application.rb using a monkey patch

config/discourse_defaults.conf

@@ -10,16 +10,13 @@
 # 2. You can copy this file to config/discourse.conf and amend with your settings
 # 3. You can pass in config from your environment, all the settings below are available.
 #    Append DISCOURSE_ and upper case the setting in ENV. For example:
-#    to pass in db_timeout of 200 you would use DISCOURSE_DB_TIMEOUT=200
+#    to pass in db_pool of 200 you would use DISCOURSE_DB_POOL=200
 
 # All settings apply to production only
 
 # connection pool size, sidekiq is set to 5, allowing an extra 3 for bg threads
 db_pool = 8
 
-# ActiveRecord connection pool timeout in milliseconds
-db_timeout = 5000
-
 # Database connection timeout in seconds
 db_connect_timeout = 5