[INTERNAL] sap.f.IDynamicPageStickyContent: Documentation improvement
[INTERNAL] sap.f.IDynamicPageStickyContent: Documentation improvement

Documentation is changed for one of sap.f.IDynamicPageStickyContent`s
method - _returnStickyContent.

Change-Id: Ibd710374edb28c6c86a6ad8398811161efb93e12

SAP/openui5,SAP/openui5,SAP/openui5,SAP/openui5