balance_sheet: Remove custom data normalizations.

These can be supported with rewrite rules now.

conservancy_beancount/reports/balance_sheet.py

@@ -88,12 +88,6 @@ class BalanceKey(NamedTuple):
 
 
 class Balances:
-    ACCOUNT_REWRITES: Mapping[str, data.Account] = {
-        # Normalize the chart of accounts from prior FYs to the current one.
-        'Expenses:CurrencyConversion': data.Account('Income:CurrencyConversion'),
-        'Income:Donations:Released': data.Account('Equity:Funds:Restricted'),
-    }
-
     def __init__(self,
                  postings: Iterable[data.Posting],
                  start_date: datetime.date,
@@ -134,20 +128,19 @@ class Balances:
                 fund = Fund.UNRESTRICTED
             else:
                 fund = Fund.RESTRICTED
-            account = self.ACCOUNT_REWRITES.get(post.account, post.account)
             try:
-                classification_s = account.meta['classification']
+                classification_s = post.account.meta['classification']
                 if isinstance(classification_s, str):
                     classification = data.Account(classification_s)
                 else:
                     raise TypeError()
             except (KeyError, TypeError):
-                classification = account
-            if account.root_part() == 'Expenses':
+                classification = post.account
+            if post.account.root_part() == 'Expenses':
                 post_type = post.meta.get('expense-type')
             else:
                 post_type = None
-            key = BalanceKey(account, classification, period, fund, post_type)
+            key = BalanceKey(post.account, classification, period, fund, post_type)
             self.balances[key] += post.at_cost()
 
     def total(self,