Remove 'enable_xcom_deserialize_support' because its not used anywhere (apache#51639)

Author: amoghrajesh

airflow-core/newsfragments/51639.significant.rst

@@ -0,0 +1,17 @@
+``enable_xcom_deserialize_support`` configuration option has been removed.
+
+This configuration was previously marked as a security risk due to potential remote code execution vulnerabilities
+when deserializing arbitrary Python objects that came in from XComs. The removal is a security improvement since
+all custom XCom serialization/deserialization is now handled safely at the worker level, making this configuration
+unnecessary in core. Users should migrate to not setting this configuration.
+
+* Types of change
+
+  * [ ] Dag changes
+  * [x] Config changes
+  * [ ] API changes
+  * [ ] CLI changes
+  * [ ] Behaviour changes
+  * [ ] Plugin changes
+  * [ ] Dependency changes
+  * [ ] Code interface changes

airflow-core/src/airflow/config_templates/config.yml

@@ -1430,15 +1430,6 @@ api:
       version_added: 2.2.0
       example: ~
       default: ""
-    enable_xcom_deserialize_support:
-      description: |
-        Indicates whether the **xcomEntries** endpoint supports the **deserialize**
-        flag. If set to ``False``, setting this flag in a request would result in a
-        400 Bad Request error.
-      type: boolean
-      version_added: 2.7.0
-      example: ~
-      default: "False"
     grid_view_sorting_order:
       description: |
         Sorting order in grid view. Valid values are: ``topological``, ``hierarchical_alphabetical``