Clean up ctrl surface API

Remove unused fields, no mandatory surfaces

libs/ctrl-interface/control_protocol/control_protocol/control_protocol.h

@@ -173,10 +173,7 @@ class ControlProtocolDescriptor
 public:
 	const char* name;              /* descriptive */
 	const char* id;                /* unique and version-specific */
-	void*       ptr;               /* protocol can store a value here */
 	void*       module;            /* not for public access */
-	int         mandatory;         /* if non-zero, always load and do not make optional */
-	bool        supports_feedback; /* if true, protocol has toggleable feedback mechanism */
 	bool (*probe) (ControlProtocolDescriptor*);
 	ControlProtocol* (*initialize) (ControlProtocolDescriptor*, Session*);
 	void (*destroy) (ControlProtocolDescriptor*, ControlProtocol*);