You cannot hide Calendar functionality from UI. (both in RUI or HTML5 )
SAP Hybris Cloud for Customer
Calendar functionality cannot be hidden in any UI because it is a mandatory utility for business to track and is part of the Built-in Support which can be used in many business objects to show associated date.
This is standard behavior in current system.
canlendar hide , KBA , LOD-CRM-CAL , Calendar Control , How To