remove AEADDecryptionContext per review.

decryption will return AEADCipherContext and encryption returns
AEADEncryptionContext
diff --git a/cryptography/hazmat/bindings/openssl/backend.py b/cryptography/hazmat/bindings/openssl/backend.py
index 7d3eb3d..1b19dda 100644
--- a/cryptography/hazmat/bindings/openssl/backend.py
+++ b/cryptography/hazmat/bindings/openssl/backend.py
@@ -240,7 +240,6 @@
 @utils.register_interface(interfaces.CipherContext)
 @utils.register_interface(interfaces.AEADCipherContext)
 @utils.register_interface(interfaces.AEADEncryptionContext)
-@utils.register_interface(interfaces.AEADDecryptionContext)
 class _CipherContext(object):
     _ENCRYPT = 1
     _DECRYPT = 0
diff --git a/cryptography/hazmat/primitives/ciphers/base.py b/cryptography/hazmat/primitives/ciphers/base.py
index cdaf2c0..b8615cb 100644
--- a/cryptography/hazmat/primitives/ciphers/base.py
+++ b/cryptography/hazmat/primitives/ciphers/base.py
@@ -46,7 +46,7 @@
             if encrypt:
                 return _AEADEncryptionContext(ctx)
             else:
-                return _AEADDecryptionContext(ctx)
+                return _AEADCipherContext(ctx)
         else:
             return _CipherContext(ctx)
 
@@ -99,11 +99,6 @@
         self._ctx.authenticate_additional_data(data)
 
 
-@utils.register_interface(interfaces.AEADDecryptionContext)
-class _AEADDecryptionContext(_AEADCipherContext):
-    pass
-
-
 @utils.register_interface(interfaces.AEADEncryptionContext)
 class _AEADEncryptionContext(_AEADCipherContext):
     @property
diff --git a/cryptography/hazmat/primitives/interfaces.py b/cryptography/hazmat/primitives/interfaces.py
index 582876f..e3f4f58 100644
--- a/cryptography/hazmat/primitives/interfaces.py
+++ b/cryptography/hazmat/primitives/interfaces.py
@@ -94,10 +94,6 @@
         """
 
 
-class AEADDecryptionContext(six.with_metaclass(abc.ABCMeta)):
-    pass
-
-
 class PaddingContext(six.with_metaclass(abc.ABCMeta)):
     @abc.abstractmethod
     def update(self, data):