Remove therubyracer gem (unused)

Gemfile

@@ -10,9 +10,6 @@ gem 'sass-rails', '~> 5.0'
 # Use Uglifier as compressor for JavaScript assets
 gem 'uglifier', '>= 1.3.0'
 
-# See https://github.com/sstephenson/execjs#readme for more supported runtimes
-gem 'therubyracer', platforms: :ruby
-
 # Use jquery as the JavaScript library
 gem 'jquery-rails'
 # Turbolinks makes following links in your web application faster. Read more: https://github.com/rails/turbolinks

Gemfile.lock

@@ -352,7 +352,6 @@ GEM
     leaflet-markercluster-rails (0.7.0)
       railties (>= 3.1)
     leaflet-rails (0.7.7)
-    libv8 (3.16.14.17)
     listen (3.1.5)
       rb-fsevent (~> 0.9, >= 0.9.4)
       rb-inotify (~> 0.9, >= 0.9.7)
@@ -473,7 +472,6 @@ GEM
       trollop (~> 2.1)
     rdoc (4.3.0)
     redis (3.3.0)
-    ref (2.0.0)
     request_store (1.3.1)
     responders (2.3.0)
       railties (>= 4.2.0, < 5.1)
@@ -586,9 +584,6 @@ GEM
       httpclient (>= 2.4)
       i18n
       json (>= 1.4.3)
-    therubyracer (0.12.2)
-      libv8 (~> 3.16.14.0)
-      ref
     thor (0.19.4)
     thread_safe (0.3.5)
     tilt (2.0.5)
@@ -716,7 +711,6 @@ DEPENDENCIES
   spring
   spring-commands-rspec
   sqlite3
-  therubyracer
   timecop
   turbolinks (~> 2.5)
   uglifier (>= 1.3.0)