Remove protected_attributes gem

We cleaned up all the `attr_accessible` calls, hooray! This was blocking us from upgrading to Rails 5, so now we can!

Gemfile

@@ -69,7 +69,6 @@ gem 'uglifier',      ">= 1.0.3"
 # Backfills for old Rails behaviors
 # TODO: Would be nice to become canonical and not need these!
 gem 'rails-observers', '~> 0.1.5'
-gem 'protected_attributes', '~> 1.1', '>= 1.1.4'
 
 group :development do
   gem 'capistrano', '~> 2.15.5', require: false

Gemfile.lock

@@ -159,8 +159,6 @@ GEM
     orm_adapter (0.5.0)
     parallel (1.13.0)
     passenger_monit (0.1.1)
-    protected_attributes (1.1.4)
-      activemodel (>= 4.0.1, < 5.0)
     rack (1.5.5)
     rack-attack (2.2.1)
       rack
@@ -306,7 +304,6 @@ DEPENDENCIES
   openneo-auth-signatory (~> 0.1.0)
   parallel (~> 1.13.0)
   passenger_monit (~> 0.1.1)
-  protected_attributes (~> 1.1, >= 1.1.4)
   rack-attack (~> 2.2.0)
   rails (= 4.0.13)
   rails-i18n (~> 4.0, >= 4.0.9)