Kill some commented out code and other cleanups (#649)

diff --git a/src/OpenSSL/crypto.py b/src/OpenSSL/crypto.py
index 5803ae9..e58a455 100644
--- a/src/OpenSSL/crypto.py
+++ b/src/OpenSSL/crypto.py
@@ -739,23 +739,9 @@
     }
 
     def _subjectAltNameString(self):
-        method = _lib.X509V3_EXT_get(self._extension)
-        _openssl_assert(method != _ffi.NULL)
-        ext_data = _lib.X509_EXTENSION_get_data(self._extension)
-        payload = ext_data.data
-        length = ext_data.length
-
-        payloadptr = _ffi.new("unsigned char**")
-        payloadptr[0] = payload
-
-        if method.it != _ffi.NULL:
-            ptr = _lib.ASN1_ITEM_ptr(method.it)
-            data = _lib.ASN1_item_d2i(_ffi.NULL, payloadptr, length, ptr)
-            names = _ffi.cast("GENERAL_NAMES*", data)
-        else:
-            names = _ffi.cast(
-                "GENERAL_NAMES*",
-                method.d2i(_ffi.NULL, payloadptr, length))
+        names = _ffi.cast(
+            "GENERAL_NAMES*", _lib.X509V3_EXT_d2i(self._extension)
+        )
 
         names = _ffi.gc(names, _lib.GENERAL_NAMES_free)
         parts = []