support: Set discounted price instead percentage for customers.

This allows us to set the price of a plan exactly as discussed with
the customer.

zerver/lib/validator.py

@@ -31,7 +31,6 @@ for any particular type of object.
 import re
 from dataclasses import dataclass
 from datetime import datetime, timezone
-from decimal import Decimal
 from typing import (
     Any,
     Callable,
@@ -605,10 +604,6 @@ def to_float(var_name: str, s: str) -> float:
     return float(s)
 
 
-def to_decimal(var_name: str, s: str) -> Decimal:
-    return Decimal(s)
-
-
 def to_timezone_or_empty(var_name: str, s: str) -> str:
     try:
         s = canonicalize_timezone(s)