No longer provide a feature in test-helper.el

The file isn't a library intended to be loaded with `require`.
Instead `ert-runner` loads it using `load`.  Other packages that
use `ert-runner` also come with a file named test-helper.el and
unfortunately many of those also provide `test-helper`, which
leads to conflicts.

Fixes #390.

Author: tarsius

test/elixir-mode-font-test.el

@@ -8,8 +8,6 @@
 
 ;;; Code:
 
-(require 'test-helper)
-
 (defun elixir-test-face-at (pos &optional content)
   "Get the face at POS in CONTENT.
 

test/elixir-mode-indentation-test.el

@@ -9,8 +9,6 @@
 
 ;;; Code:
 
-(require 'test-helper)
-
 (elixir-def-indentation-test indent-use-dot-module-newline
                              (:tags '(indentation))
   "defmodule Foo do

test/elixir-mode-moving-test.el

@@ -2,8 +2,6 @@
 
 ;;; Code:
 
-(require 'test-helper)
-
 (ert-deftest beginning-of-defun ()
   :tags '(moving)
   (elixir-test-with-temp-buffer

test/test-helper.el

@@ -63,6 +63,4 @@
   (defun ert-runner/run-tests-batch-and-exit (selector)
     (ert-run-tests-interactively selector)))
 
-(provide 'test-helper)
-
 ;;; test-helper.el ends here