Remove excessive "M" and "N" fields, PositiveInteger is sufficient.

nucypher/characters/control/specifications/alice.py

@@ -42,10 +42,10 @@ class PolicyBaseSchema(BaseSchema):
             '-bvk',
             help="Bob's verifying key as a hexadecimal string",
             type=click.STRING, required=False))
-    threshold = character_fields.Threshold(
+    threshold = base_fields.PositiveInteger(
         required=True, load_only=True,
         click=options.option_threshold)
-    shares = character_fields.Shares(
+    shares = base_fields.PositiveInteger(
         required=True, load_only=True,
         click=options.option_shares)
     expiration = character_fields.DateTime(

nucypher/characters/control/specifications/fields/misc.py

@@ -15,17 +15,9 @@
  along with nucypher.  If not, see <https://www.gnu.org/licenses/>.
 """
 
-from nucypher.control.specifications.fields.base import Integer, PositiveInteger
+from nucypher.control.specifications.fields.base import Integer
 from nucypher.cli import types
 
 
-class Threshold(PositiveInteger):
-    pass
-
-
-class Shares(PositiveInteger):
-    pass
-
-
 class Wei(Integer):
     click_type = types.WEI