Revert "Add global toggle to use_cassette."

This reverts commit 366e2b75bb.

Conflicts:
	tests/unit/test_cassettes.py

vcr/cassette.py

@@ -14,33 +14,15 @@ from .matchers import requests_match, uri, method
 from .errors import UnhandledHTTPRequestError
 
 
-class NullContextDecorator(object):
-
-    def __init__(self, *args, **kwargs):
-        pass
-
-    def __enter__(self, *args):
-        return self
-
-    def __exit__(self, *args):
-        pass
-
-    def __call__(self, function):
-        return function
-
-
 class use_cassette(object):
 
-    _enabled = True
-
     def __init__(self, cls, *args, **kwargs):
         self.args = args
         self.kwargs = kwargs
         self.cls = cls
 
     def __enter__(self):
-        self._cassette = self.cls.load(*self.args, **self.kwargs) if self._enabled \
-                         else NullContextDecorator()
+        self._cassette = self.cls.load(*self.args, **self.kwargs)
         return self._cassette.__enter__()
 
     def __exit__(self, *args):