Remove serialization module

Serialization api is removed from securesystemslib with this
commit because of its complexity and don't having a use case
for a standalone securesystemslib Envelope.

This commit removes `_default_deserializer`, `_default_serializer`
and `get_payload` methods of Envelope with securesystemslib but
keeps `from_dict` and `to_dict` methods to be consistent with
other metadata related classes, e.g. signer.

Signed-off-by: Pradyumna Krishna <[email protected]>

securesystemslib/dsse.py

@@ -5,45 +5,13 @@
 from typing import Any, Dict, List
 
 from securesystemslib import exceptions
-from securesystemslib.serialization import (
-    BaseDeserializer,
-    BaseSerializer,
-    JSONDeserializer,
-    JSONSerializable,
-    JSONSerializer,
-    SerializationMixin,
-)
 from securesystemslib._internal.utils import b64enc, b64dec
 from securesystemslib.signer import Key, Signature, Signer
 
 logger = logging.getLogger(__name__)
 
 
-class EnvelopeJSONDeserializer(JSONDeserializer):
-    """Deserializes raw bytes and creates an Envelope object using JSON
-    Deserialization."""
-
-    def deserialize(self, raw_data: bytes) -> "Envelope":
-        """Deserialize utf-8 encoded JSON bytes into an instance of Envelope.
-
-        Arguments:
-            raw_data: A utf-8 encoded bytes string.
-
-        Raises:
-            DeserializationError: If fails to deserialize raw_data.
-
-        Returns:
-            dict.
-        """
-        try:
-            return Envelope.from_dict(super().deserialize(raw_data))
-        except Exception as e:
-            raise exceptions.DeserializationError(
-                "Failed to create Envelope"
-            ) from e
-
-
-class Envelope(SerializationMixin, JSONSerializable):
+class Envelope:
     """DSSE Envelope to provide interface for signing arbitrary data.
 
     Attributes:
@@ -70,14 +38,6 @@ def __eq__(self, other: Any) -> bool:
             and self.signatures == other.signatures
         )
 
-    @staticmethod
-    def _default_deserializer() -> BaseDeserializer:
-        return EnvelopeJSONDeserializer()
-
-    @staticmethod
-    def _default_serializer() -> BaseSerializer:
-        return JSONSerializer()
-
     @classmethod
     def from_dict(cls, data: dict) -> "Envelope":
         """Creates a DSSE Envelope from its JSON/dict representation.
@@ -197,21 +157,3 @@ def verify(self, keys: List[Key], threshold: int) -> Dict[str, Key]:
             )
 
         return accepted_keys
-
-    def get_payload(
-        self,
-        deserializer: BaseDeserializer,
-    ) -> Any:
-        """Parse DSSE payload.
-
-        Arguments:
-            deserializer: ``BaseDeserializer`` implementation to use.
-
-        Raises:
-            DeserializationError: The payload cannot be deserialized.
-
-        Returns:
-            The deserialized object of payload.
-        """
-
-        return deserializer.deserialize(self.payload)