remove sprockets-es6 and execjs dependencies

Gemfile

@@ -7,7 +7,6 @@ gem 'rails-deprecated_sanitizer', '~> 1.0.3'
 gem 'responders', '~> 2.0'
 
 gem 'sprockets', '~> 3.7.0'
-gem 'sprockets-es6', '~> 0.9.2'
 
 # Default values for AR models
 gem 'default_value_for', '~> 3.0.0'

Gemfile.lock

@@ -72,10 +72,6 @@ GEM
       descendants_tracker (~> 0.0.4)
       ice_nine (~> 0.11.0)
       thread_safe (~> 0.3, >= 0.3.1)
-    babel-source (5.8.35)
-    babel-transpiler (0.7.0)
-      babel-source (>= 4.0, < 6)
-      execjs (~> 2.0)
     babosa (1.0.2)
     base32 (0.3.2)
     bcrypt (3.1.11)
@@ -733,10 +729,6 @@ GEM
     sprockets (3.7.0)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
-    sprockets-es6 (0.9.2)
-      babel-source (>= 5.8.11)
-      babel-transpiler
-      sprockets (>= 3.0.0)
     sprockets-rails (3.1.1)
       actionpack (>= 4.0)
       activesupport (>= 4.0)
@@ -986,7 +978,6 @@ DEPENDENCIES
   spring-commands-rspec (~> 1.0.4)
   spring-commands-spinach (~> 1.1.0)
   sprockets (~> 3.7.0)
-  sprockets-es6 (~> 0.9.2)
   stackprof (~> 0.2.10)
   state_machines-activerecord (~> 0.4.0)
   sys-filesystem (~> 1.1.6)