Fix Rubocop offenses

app/controllers/submissions_controller.rb

@@ -40,7 +40,7 @@ class SubmissionsController < ApplicationController
       # zip .co file
       zio.put_next_entry('.co')
       zio.write(File.read(id_file))
-      File.delete(id_file) if File.exist?(id_file)
+      FileUtils.rm_rf(id_file)
 
       # zip client scripts
       scripts_path = 'app/assets/remote_scripts'

app/models/runner.rb

@@ -154,13 +154,13 @@ class Runner < ApplicationRecord
       rescue Runner::Error
         # An additional error was raised during synchronization
         raise Runner::Error::EnvironmentNotFound.new(
-          "The execution environment with id #{execution_environment.id} was not found by the runner management. "\
+          "The execution environment with id #{execution_environment.id} was not found by the runner management. " \
           'In addition, it could not be synced so that this probably indicates a permanent error.'
         )
       else
         # No error was raised during synchronization
         raise Runner::Error::EnvironmentNotFound.new(
-          "The execution environment with id #{execution_environment.id} was not found yet by the runner management. "\
+          "The execution environment with id #{execution_environment.id} was not found yet by the runner management. " \
           'It has been successfully synced now so that the next request should be successful.'
         )
       end