Deprecate Classic API Notepads. Mark task_set/get_note() with
the deprecated attribute, and also mark the notepads field.
Replace disable with enable option for notepads in confdefs.h,
and make notepads disabled by default. The previous option
CONFIGURE_DISABLE_CLASSIC_API_NOTEPADS is now unused and
will emit a compile-time warning. A new option
CONFIGURE_ENABLE_CLASSIC_API_NOTEPADS is available to turn
on notepads, but it also will emit a compile-time warning
to indicate that notepads are deprecated.
Closes#2265
3ac681191e
