Remove mini_racer gem (#12387)

Gemfile

@@ -145,7 +145,6 @@ group :development, :test do
   gem "dotenv-rails", "~> 2.7.6" # For loading ENV variables locally
   gem "faker", "~> 2.15" # A library for generating fake data such as names, addresses, and phone numbers
   gem "knapsack_pro", "~> 2.11.0" # Help parallelize Ruby spec builds
-  gem "mini_racer", "~> 0.3.1" # Minimal embedded v8
   gem "pry-byebug", "~> 3.8" # Combine 'pry' with 'byebug'. Adds 'step', 'next', 'finish', 'continue' and 'break' commands to control execution
   gem "rspec-rails", "~> 4.0" # rspec-rails is a testing framework for Rails 3+
   gem "rubocop", "~> 1.8", require: false # Automatic Ruby code style checking tool

Gemfile.lock

@@ -433,10 +433,6 @@ GEM
     libhoney (1.17.0)
       addressable (~> 2.0)
       http (>= 2.0, < 5.0)
-    libv8 (8.4.255.0)
-    libv8 (8.4.255.0-x86_64-darwin-19)
-    libv8 (8.4.255.0-x86_64-darwin-20)
-    libv8 (8.4.255.0-x86_64-linux)
     liquid (5.0.0)
     listen (3.4.1)
       rb-fsevent (~> 0.10, >= 0.10.3)
@@ -461,8 +457,6 @@ GEM
     mini_magick (4.11.0)
     mini_mime (1.0.2)
     mini_portile2 (2.5.0)
-    mini_racer (0.3.1)
-      libv8 (~> 8.4.255)
     minitest (5.14.3)
     msgpack (1.3.3)
     multi_json (1.15.0)
@@ -917,7 +911,6 @@ DEPENDENCIES
   liquid (~> 5.0)
   listen (~> 3.4)
   memory_profiler (~> 1.0)
-  mini_racer (~> 0.3.1)
   nakayoshi_fork (~> 0.0.4)
   nokogiri (~> 1.11)
   octokit (~> 4.20)