[ML] Removing unused include_model_definition type (elastic#204420)

`include_model_definition` has been deprecated in favor of
`include=definition`
Although `include_model_definition` was included in the type for the
client side `getTrainedModels`, the argument was not part of the
endpoint schema and would have caused an error if used.
In the future if we need this adding to the endpoint it can be added
then.

x-pack/platform/plugins/shared/ml/public/application/services/ml_api_service/trained_models.ts

@@ -31,7 +31,6 @@ import type {
 
 export interface InferenceQueryParams {
   from?: number;
-  include_model_definition?: boolean;
   size?: number;
   tags?: string;
   include?: 'total_feature_importance' | 'feature_importance_baseline' | string;