Straight up to your questions:
To remove the "Please provide an AppointmentsSource" you need to change/remove the TextBlock value in the AppointmentSourceWarning Grid in the theme. Here is a snipped code representing that:
"Please provide an AppointmentsSource"
On your second question, you can remove the delete button with x:Name="DeleteButton"
in the theme you are using.
The easiest way to customize the ScheduleView theme is to use implicit styles, you can read this article
for more details.
the Telerik team
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