Remove ContentCredentials from API

src/proto/generation.proto

@@ -242,16 +242,6 @@ message T2IAdapterParameter {
  T2IAdapterInit adapter_init_type = 3;
 }
 
-message ContentCredentialsParameters {
- enum ModelMetadata {
- MODEL_METADATA_UNSPECIFIED = 0;
- MODEL_METADATA_SIGN_WITH_ENGINE_ID = 1;
- }
- oneof parameters {
- ModelMetadata model_metadata = 1;
- }
-}
-
 // FineTuningParameters specify which fine-tuned models to use for generation.
 message FineTuningParameters {
  // The id of the fine-tuned model to generate content from.
@@ -277,8 +267,7 @@ message ImageParameters {
  optional bool quantize = 10; //defaults to true
  optional T2IAdapterParameter adapter = 12;
  repeated FineTuningParameters fine_tuning_parameters = 13; 
- optional ContentCredentialsParameters content_credentials_parameters = 14; // Set field to have image signed by C2PA
- reserved 11;
+ reserved 11, 14;
  // next available tag: 15
 }