Remove Coveralls

Coveralls is fine, but it's interfering with Travis somehow.

test/coverage_setup.rb

@@ -1,15 +0,0 @@
-begin
-  require 'simplecov'
-  require 'coveralls'
-
-  SimpleCov.formatter = SimpleCov::Formatter::MultiFormatter[
-    SimpleCov::Formatter::HTMLFormatter,
-    Coveralls::SimpleCov::Formatter
-  ]
-
-  SimpleCov.start do
-    add_group "lib", "lib"
-    add_group "test", "test"
-  end
-rescue LoadError
-end

test/test_helper.rb

@@ -1,5 +1,4 @@
 require 'bundler/setup'
-require 'coverage_setup' if ENV["CI"]
 require 'minitest/autorun'
 require 'active_model_serializers'
 require 'fixtures/poro'