Remove the context argument from Managed::delete(Indexed)Property

Remove the context argument from Managed::delete(Indexed)Property

It's not required, as we can always get the current context from
the Managed object for the cases we need it.

Change-Id: I29fb9861a73ece1b3d5aa45f3bc350d8a5f76fa9
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>