Change copyright statements from 2020 to 2021

v2_28_0/CDT-commonTypes-v2_28_0.xsd

v2_28_0/CDT-container-v2_28_0.xsd

v2_28_0/CDT-contentInstance-v2_28_0.xsd

v2_28_0/CDT-delivery-v2_28_0.xsd

v2_28_0/CDT-deviceCapability-v2_28_0.xsd

v2_28_0/CDT-deviceInfo-v2_28_0.xsd

v2_28_0/CDT-dynamicAuthorizationConsultation-v2_28_0.xsd

v2_28_0/CDT-enumerationTypes-v2_28_0.xsd

v2_28_0/CDT-eventConfig-v2_28_0.xsd

v2_28_0/CDT-eventLog-v2_28_0.xsd

v2_28_0/CDT-execInstance-v2_28_0.xsd

v2_28_0/CDT-firmware-v2_28_0.xsd

v2_28_0/CDT-genericInterworkingOperationInstance-v2_28_0.xsd

v2_28_0/CDT-genericInterworkingService-v2_28_0.xsd

v2_28_0/CDT-group-v2_28_0.xsd

v2_28_0/CDT-locationPolicy-v2_28_0.xsd

v2_28_0/CDT-m2mServiceSubscriptionProfile-v2_28_0.xsd

v2_28_0/CDT-memory-v2_28_0.xsd

v2_28_0/CDT-mgmtCmd-v2_28_0.xsd

v2_28_0/CDT-node-v2_28_0.xsd