Remove unused constants to avoid warnings

Author: ksperling-apple

src/darwin/Framework/CHIP/MTRDeviceController.mm

@@ -88,13 +88,10 @@
 static NSString * const kErrorPairingInit = @"Init failure while creating a pairing delegate";
 static NSString * const kErrorPartialDacVerifierInit = @"Init failure while creating a partial DAC verifier";
 static NSString * const kErrorPairDevice = @"Failure while pairing the device";
-static NSString * const kErrorUnpairDevice = @"Failure while unpairing the device";
 static NSString * const kErrorStopPairing = @"Failure while trying to stop the pairing process";
 static NSString * const kErrorPreWarmCommissioning = @"Failure while trying to pre-warm the commissioning process";
 static NSString * const kErrorOpenPairingWindow = @"Open Pairing Window failed";
-static NSString * const kErrorGetPairedDevice = @"Failure while trying to retrieve a paired device";
 static NSString * const kErrorNotRunning = @"Controller is not running. Call startup first.";
-static NSString * const kInfoStackShutdown = @"Shutting down the Matter Stack";
 static NSString * const kErrorSetupCodeGen = @"Generating Manual Pairing Code failed";
 static NSString * const kErrorGenerateNOC = @"Generating operational certificate failed";
 static NSString * const kErrorKeyAllocation = @"Generating new operational key failed";