Remove redundant cache being stopped check

Signed-off-by: Michal Mielewczyk <michal.mielewczyk@intel.com>

modules/include/cas_ioctl_codes.h

@@ -598,9 +598,6 @@ enum kcas_error {
 	/** Waiting for async operation was interrupted */
 	KCAS_ERR_WAITING_INTERRUPTED,
 
-	/** Cache already being stopped*/
-	KCAS_ERR_CACHE_STOPPING,
-
 	/** Core device is in active state */
 	KCAS_ERR_CORE_IN_ACTIVE_STATE
 };