FilterWheel: remove deprecated position setting.

Getting and setting a filterwheel from the device settings has been
deprecated for a while and the related get/set methods have been
around since forever.  Cockpit now also uses the getter and setter
methods which was the only reason this was not removed before.

This commit removes the position setting.

NEWS.rst

@@ -23,6 +23,9 @@ Version 0.7.0 (upcoming)
     removed from the base class and is now only kept by cameras that
     actually make use of it, namely, ``PVCamera`` and ``AndorAtmcd``.
 
+  * All filterwheels had a ``"position"`` setting which was redundant
+    with the related get/set methods.  The setting was been removed.
+
 * New devices supported:
 
   * Hamamatsu cameras (:class:`microscope.cameras.hamamatsu.HamamatsuCamera`)

microscope/abc.py

@@ -1265,16 +1265,6 @@ def __init__(self, positions: int, **kwargs) -> None:
                 "positions must be a positive number (was %d)" % positions
             )
         self._positions = positions
-        # The position as an integer.
-        # Deprecated: clients should call get_position and set_position;
-        # still exposed as a setting until cockpit uses set_position.
-        self.add_setting(
-            "position",
-            "int",
-            self.get_position,
-            self.set_position,
-            lambda: (0, self.get_num_positions()),
-        )
 
     @property
     def n_positions(self) -> int: