Remove "non-validating" backend

It's been superseded by the VALIDATE_ON_ACCESS setting

imagekit/imagecache/__init__.py

@@ -1,5 +1,5 @@
 from ..utils import get_singleton
-from .base import InvalidImageCacheBackendError, PessimisticImageCacheBackend, NonValidatingImageCacheBackend
+from .base import InvalidImageCacheBackendError, PessimisticImageCacheBackend
 
 
 def get_default_image_cache_backend():
@@ -9,4 +9,4 @@ def get_default_image_cache_backend():
     """
     from django.conf import settings
     return get_singleton(settings.IMAGEKIT_DEFAULT_IMAGE_CACHE_BACKEND,
-            'validation backend')
+            'image cache backend')

imagekit/imagecache/base.py

@@ -31,30 +31,3 @@ class PessimisticImageCacheBackend(object):
 
     def clear(self, file):
         file.delete(save=False)
-
-
-class NonValidatingImageCacheBackend(object):
-    """
-    A backend that is super optimistic about the existence of spec files. It
-    will hit your file storage much less frequently than the pessimistic
-    backend, but it is technically possible for a cache file to be missing
-    after validation.
-
-    """
-
-    def validate(self, file):
-        """
-        NonValidatingImageCacheBackend has faith, so validate's a no-op.
-
-        """
-        pass
-
-    def invalidate(self, file):
-        """
-        Immediately generate a new spec file upon invalidation.
-
-        """
-        file.generate(save=True)
-
-    def clear(self, file):
-        file.delete(save=False)