Fix grammar issue in error message

components/application-mgt/org.wso2.carbon.device.application.mgt.core/src/main/java/org/wso2/carbon/device/application/mgt/core/impl/ApplicationManagerImpl.java

@@ -1801,7 +1801,7 @@ public class ApplicationManagerImpl implements ApplicationManager {
         try {
             DeviceType deviceType = deviceManagementProviderService.getDeviceType(deviceTypeName);
             if (deviceType == null) {
-                String msg = "Device type doesn't not exist. Hence check the application name existence with valid "
+                String msg = "Device type doesn't exist. Hence check the application name existence with valid "
                         + "device type name.";
                 log.error(msg);
                 throw new BadRequestException(msg);