bmm150: Remove broken reset function.

Looks like copy-pasta from bmi270 driver.

There is a soft reset capability documented in the BMM150 datasheet, but it
uses different register bits and I don't have a BMM150 at hand to test it.

Found by Ruff checking F821.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

micropython/drivers/imu/bmm150/bmm150.py

@@ -165,9 +165,6 @@ class BMM150:
             z = (z5 / (z4 * 4)) / 16
         return z
 
-    def reset(self):
-        self._write_reg(_CMD, 0xB6)
-
     def magnet_raw(self):
         for i in range(0, 10):
             self._read_reg_into(_DATA, self.scratch)