Remove unnecessary check in bigint division.

runtime/lib/bigint.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Copyright 2009 The Go Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
 /*
  * Copyright (c) 2003-2005  Tom Wu
@@ skipping 863 matching lines @@
     }
     while (--j >= 0) {
       // Estimate quotient digit.
       var qd;
       if (r._digits[--i] == y0) {
         qd = DIGIT_MASK;
       } else {
         // Chop off one bit, since a Mint cannot hold 2 DIGITs.
         qd = ((r._digits[i] << (DIGIT_BITS - 1)) |
               (r._digits[i - 1] >> 1)) ~/ yt;
-        if (qd > DIGIT_MASK) {
-          qd = DIGIT_MASK;
-        }
       }
       if ((r._digits[i] += y._am(0, qd, r, j, y_used)) < qd) {  // Try it out.
         y._dlShiftTo(j, t);
         r._subTo(t, r);
         while (r._digits[i] < --qd) {
           r._subTo(t, r);
         }
       }
     }
     if (q != null) {
@@ skipping 448 matching lines @@
   void _sqrTo(_Bigint x, _Bigint r) {
     x._sqrTo(r);
     _reduce(r);
   }
 
   void _mulTo(_Bigint x, _Bigint y, _Bigint r) {
     x._mulTo(y, r);
     _reduce(r);
   }
 }