tools: remove simplejson dependency

As Node.js expects either Python 2.6 or 2.7 installed to work properly,
simplejson module is no longer necessary. It was included in Python 2.6
as the json module.

PR-URL: #6101
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Benjamin Gruenbaum <benjamingr@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>

tools/install.py

@@ -1,12 +1,7 @@
 #!/usr/bin/env python
 
 import errno
-
-try:
-  import json
-except ImportError:
-  import simplejson as json
-
+import json
 import os
 import re
 import shutil