stepper: Remove min_stop_interval from mcu code

Now that the host never uses a min_stop_interval, remove it from the
mcu code.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/mcu.py

@@ -824,7 +824,7 @@ class MCU:
         return False, '%s: %s' % (self._name, stats)
 
 Common_MCU_errors = {
-    ("Timer too close", "No next step"): """
+    ("Timer too close",): """
 This often indicates the host computer is overloaded. Check
 for other processes consuming excessive CPU time, high swap
 usage, disk errors, overheating, unstable voltage, or