dice: remove dead code for addition argument to DicePouch

The equation evaluator has been taking care of this since 2013, when the
`addition` argument was hard-coded to `0` in a dice-rolling rewrite. See
commit 5a8ecf4 for some of the history.

A decade later, in 2023, we have no use for this argument. The code to
handle it is unreachable, which affects the plugin's coverage score.
Best solution is to just remove the dead code.

sopel/modules/dice.py

@@ -17,17 +17,15 @@
 
 
 class DicePouch:
-    def __init__(self, num_of_die, type_of_die, addition):
+    def __init__(self, num_of_die, type_of_die):
         """Initialize dice pouch and roll the dice.
 
         Args:
             num_of_die: number of dice in the pouch.
             type_of_die: how many faces the dice have.
-            addition: how much is added to the result of the dice.
         """
         self.num = num_of_die
         self.type = type_of_die
-        self.addition = addition
 
         self.dice = {}
         self.dropped = {}
@@ -70,7 +68,7 @@ def drop_lowest(self, n):
                 del self.dice[i]
 
     def get_simple_string(self):
-        """Return the values of the dice like (2+2+2[+1+1])+1."""
+        """Return the values of the dice like (2+2+2[+1+1])."""
         dice = self.dice.items()
         faces = ("+".join([str(face)] * times) for face, times in dice)
         dice_str = "+".join(faces)
@@ -81,14 +79,10 @@ def get_simple_string(self):
             dfaces = ("+".join([str(face)] * times) for face, times in dropped)
             dropped_str = "[+%s]" % ("+".join(dfaces),)
 
-        plus_str = ""
-        if self.addition:
-            plus_str = "{:+d}".format(self.addition)
-
-        return "(%s%s)%s" % (dice_str, dropped_str, plus_str)
+        return "(%s%s)" % (dice_str, dropped_str)
 
     def get_compressed_string(self):
-        """Return the values of the dice like (3x2[+2x1])+1."""
+        """Return the values of the dice like (3x2[+2x1])."""
         dice = self.dice.items()
         faces = ("%dx%d" % (times, face) for face, times in dice)
         dice_str = "+".join(faces)
@@ -99,15 +93,11 @@ def get_compressed_string(self):
             dfaces = ("%dx%d" % (times, face) for face, times in dropped)
             dropped_str = "[+%s]" % ("+".join(dfaces),)
 
-        plus_str = ""
-        if self.addition:
-            plus_str = "{:+d}".format(self.addition)
-
-        return "(%s%s)%s" % (dice_str, dropped_str, plus_str)
+        return "(%s%s)" % (dice_str, dropped_str)
 
     def get_sum(self):
-        """Get the sum of non-dropped dice and the addition."""
-        result = self.addition
+        """Get the sum of non-dropped dice."""
+        result = 0
         for face, times in self.dice.items():
             result += face * times
         return result
@@ -155,7 +145,7 @@ def _roll_dice(bot, dice_expression):
         bot.reply('I only have 1000 dice. =(')
         return None  # Signal there was a problem
 
-    dice = DicePouch(dice_num, dice_type, 0)
+    dice = DicePouch(dice_num, dice_type)
 
     if result.group('drop_lowest'):
         drop = int(result.group('drop_lowest'))