remove duplicate key symbols from MTRDevice_Concrete

Author: kiel-apple

src/darwin/Framework/CHIP/MTRDevice_Concrete.mm

@@ -69,9 +69,6 @@ @interface MTRDevice_Concrete ()
 
 typedef void (^MTRDeviceAttributeReportHandler)(NSArray * _Nonnull);
 
-NSString * const MTRPreviousDataKey = @"previousData";
-NSString * const MTRDataVersionKey = @"dataVersion";
-
 #define kSecondsToWaitBeforeMarkingUnreachableAfterSettingUpSubscription 10
 
 // Disabling pending crashes