Remove cdecimal dependency

It is no more needed as it is standard under Python3

INSTALL

@@ -7,7 +7,6 @@ Prerequisites
  * Python 3.4 or later (http://www.python.org/)
  * python-dateutil (http://labix.org/python-dateutil)
  * Optional: trytond (http://www.tryton.org/)
- * Optional: cdecimal (http://www.bytereef.org/mpdecimal/index.html)
 
 Installation
 ------------

proteus/__init__.py

@@ -4,14 +4,6 @@
 A library to access Tryton's models like a client.
 '''
 import sys
-try:
-    import cdecimal
-    # Use cdecimal globally
-    if 'decimal' not in sys.modules:
-        sys.modules['decimal'] = cdecimal
-except ImportError:
-    import decimal
-    sys.modules['cdecimal'] = decimal
 import threading
 import datetime
 import functools

setup.py

@@ -80,7 +80,6 @@ setup(name=name,
         ],
     extras_require={
         'trytond': [get_require_version('trytond')],
-        'cdecimal': ['cdecimal'],
         },
     dependency_links=dependency_links,
     zip_safe=True,