remove deprecation multiple warning suppressor

we don't have any more non-gem plugins, so we don't need to suppress multiple warnings for them

Change-Id: I50160a8b305235534416f1dcf2b17ded1eb89dc8
Reviewed-on: https://gerrit.instructure.com/52304
Tested-by: Jenkins
Reviewed-by: Rob Orton <rob@instructure.com>
Product-Review: Cody Cutrer <cody@instructure.com>
QA-Review: Cody Cutrer <cody@instructure.com>

config/environment.rb

@@ -7,17 +7,5 @@ end
 # Load the rails application
 require File.expand_path('../application', __FILE__)
 
-ActiveSupport::Deprecation.module_eval do
-  class << self
-    def warn_with_single_instance_check(message = nil, callstack = caller)
-      @warned ||= Set.new
-      return if @warned.include?(callstack)
-      @warned << callstack
-      warn_without_single_instance_check(message, callstack)
-    end
-    alias_method_chain :warn, :single_instance_check
-  end
-end
-
 # Initialize the rails application
 CanvasRails::Application.initialize!