[account.cpp] refactor xaccAccountGetPresentBalance

instead of starting from account->splits tail then backtrack, reuse
existing code.

libgnucash/engine/Account.cpp

@@ -3448,32 +3448,14 @@ xaccAccountGetReconciledBalanceAsOfDate (Account *acc, time64 date)
 
 /*
  * Originally gsr_account_present_balance in gnc-split-reg.c
- *
- * How does this routine compare to xaccAccountGetBalanceAsOfDate just
- * above?  These two routines should eventually be collapsed into one.
- * Perhaps the startup logic from that one, and the logic from this
- * one that walks from the tail of the split list.
  */
 gnc_numeric
 xaccAccountGetPresentBalance (const Account *acc)
 {
-    AccountPrivate *priv;
-    GList *node;
-    time64 today;
-
     g_return_val_if_fail(GNC_IS_ACCOUNT(acc), gnc_numeric_zero());
 
-    priv = GET_PRIVATE(acc);
-    today = gnc_time64_get_today_end();
-    for (node = g_list_last(priv->splits); node; node = node->prev)
-    {
-        Split *split = static_cast<Split*>(node->data);
-
-        if (xaccTransGetDate (xaccSplitGetParent (split)) <= today)
-            return xaccSplitGetBalance (split);
-    }
-
-    return gnc_numeric_zero ();
+    return xaccAccountGetBalanceAsOfDate (GNC_ACCOUNT (acc),
+                                          gnc_time64_get_today_end ());
 }