rspec: allow Rails to auto-migrate the test schema

rails_helper already has `ActiveRecord::Migration.maintain_test_schema!`
which automatically updates the test database if needed.

However, if we raise **before** `maintain_test_schema` had the chance
to do its job, the test database is never-automigrated.

Thus by removing the check, we ensure the test database will be migrated
as needed (and still an error will be raised if the schema cannot be
applied).

spec/spec_helper.rb

@@ -69,10 +69,6 @@ end
 Dir[Rails.root.join('spec', 'support', '**', '*.rb')].each { |f| require f }
 Dir[Rails.root.join('spec', 'factories', '**', '*.rb')].each { |f| require f }
 
-# Checks for pending migrations before tests are run.
-# If you are not using ActiveRecord, you can remove this line.
-ActiveRecord::Migration.check_pending! if defined?(ActiveRecord::Migration)
-
 VCR.configure do |c|
   c.ignore_localhost = true
   c.hook_into :webmock