probe: ProbePointsHelper adjustable minimum points

Factor out minimum required points check for ProbePointsHelper
in prep for setting different values for quad_gantry_level
and z_tilt_adjust

Signed-off-by: John "Fess" Fessenden <fess@fess.org>

klippy/extras/delta_calibrate.py

@@ -143,6 +143,7 @@ class DeltaCalibrate:
             points.append((math.cos(r) * dist, math.sin(r) * dist))
         self.probe_helper = probe.ProbePointsHelper(
             config, self.probe_finalize, default_points=points)
+        self.probe_helper.minimum_points(3)
         # Restore probe stable positions
         self.last_probe_positions = []
         for i in range(999):