This is the list of features which have been deprecated in SharePoint 2016:
SharePoint Foundation not included in SharePoint 2016 –There will be no free version of SharePoint 2016 offered from Microsoft. SharePoint Online may be considered as one of the alternative.
Stand-alone server installations are not allowed –Stand-alone server installations are not supported now. you will have to use MinRole feature to determine the role for the server which is being configured. For Dev/Test environment,you will have to install SQL Server before running the SharePoint Server 2016 farm configuration wizard
SharePoint 2016 & Active Directory Domain Services (AD DS) synchronization –Previously SharePoint was using FIM – ForeFront Identity Manager client to synchronize objects between SharePoint & Active Directory. In SharePoint 2016, Active Directory Import has replaced FIM as the default synchronization process. we can use MS Identity manager 2016 & third party tools for AD Synchronization.
STSADM.EXE tool has been deprecated –SharePoint 2016 will continue to support STSADM command-line tool but Windows PowerShell is recommended.
Tags & Notes are deprecated –This feature has been deprecated in SharePoint 2016 and will be removed in the next release. Though users can still create tags & notes but it is not recommended.
Excel Services –Excel services is no longer hosted in SharePoint Server. Office Online Server will be required for Excel services to run. you should be cautious while migrating from previous version of SharePoint, Office Online Server with Excel Online must be deployed so that the services that are being used are not interrupted.