Remove rails-observers

We deleted all the observers, so now we can delete this too!

Gemfile

@@ -66,10 +66,6 @@ gem 'sass-rails', '~> 5.0', '>= 5.0.7'
 gem 'compass-rails', '~> 3.1'
 gem 'uglifier', '~> 4.2'
 
-# Backfills for old Rails behaviors
-# TODO: Would be nice to become canonical and not need these!
-gem 'rails-observers', '~> 0.1.5'
-
 group :development do
   gem 'capistrano', '~> 2.15.5', require: false
   gem 'rvm-capistrano', '~> 1.5.6', require: false

Gemfile.lock

@@ -180,8 +180,6 @@ GEM
     rails-i18n (4.0.9)
       i18n (~> 0.7)
       railties (~> 4.0)
-    rails-observers (0.1.5)
-      activemodel (>= 4.0)
     railties (4.1.16)
       actionpack (= 4.1.16)
       activesupport (= 4.1.16)
@@ -308,7 +306,6 @@ DEPENDENCIES
   rack-attack (~> 2.2.0)
   rails (= 4.1.16)
   rails-i18n (~> 4.0, >= 4.0.9)
-  rails-observers (~> 0.1.5)
   rdiscount (~> 1.6.5)
   react-rails (~> 2.7, >= 2.7.1)
   resque (~> 1.23.0)