remove unused X509 certificate interface

We merged this interface and then changed our approach and use the
cryptography.x509.Certificate interface instead. This one was never
directly used.
diff --git a/docs/hazmat/backends/interfaces.rst b/docs/hazmat/backends/interfaces.rst
index a2dd0c1..e3dc96c 100644
--- a/docs/hazmat/backends/interfaces.rst
+++ b/docs/hazmat/backends/interfaces.rst
@@ -502,12 +502,10 @@
 
         :param bytes data: PEM formatted certificate data.
 
-        :returns: An instance of
-            :class:`~cryptography.hazmat.primitives.interfaces.X509Certificate`.
+        :returns: An instance of :class:`~cryptography.x509.Certificate`.
 
     .. method:: load_der_x509_certificate(data)
 
         :param bytes data: DER formatted certificate data.
 
-        :returns: An instance of
-            :class:`~cryptography.hazmat.primitives.interfaces.X509Certificate`.
+        :returns: An instance of :class:`~cryptography.x509.Certificate`.
diff --git a/src/cryptography/hazmat/primitives/interfaces/__init__.py b/src/cryptography/hazmat/primitives/interfaces/__init__.py
index 69593b4..a2154df 100644
--- a/src/cryptography/hazmat/primitives/interfaces/__init__.py
+++ b/src/cryptography/hazmat/primitives/interfaces/__init__.py
@@ -377,42 +377,3 @@
 
 # DeprecatedIn07
 CMACContext = MACContext
-
-
-@six.add_metaclass(abc.ABCMeta)
-class X509Certificate(object):
-    @abc.abstractmethod
-    def fingerprint(self, algorithm):
-        """
-        Returns bytes using digest passed.
-        """
-
-    @abc.abstractproperty
-    def serial(self):
-        """
-        Returns certificate serial number
-        """
-
-    @abc.abstractproperty
-    def version(self):
-        """
-        Returns the certificate version
-        """
-
-    @abc.abstractmethod
-    def public_key(self):
-        """
-        Returns the public key
-        """
-
-    @abc.abstractproperty
-    def not_valid_before(self):
-        """
-        Not before time (represented as UTC datetime)
-        """
-
-    @abc.abstractproperty
-    def not_valid_after(self):
-        """
-        Not after time (represented as UTC datetime)
-        """