Remove support for operator negate and replace occurrences with unary

pkg/fixnum/int32.dart

 // Copyright (c) 2012, 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.
 
 /**
  * An immutable 32-bit signed integer, in the range [-2^31, 2^31 - 1].
  * Arithmetic operations may overflow in order to maintain this range.
  */
 class int32 implements intx {
 
@@ skipping 160 matching lines @@
     return new int32.fromInt(_i + _convert(other));
   }
 
   intx operator -(other) {
     if (other is int64) {
       return this.toInt64() - other;
     }
     return new int32.fromInt(_i - _convert(other));
   }
 
-  int32 operator negate() => new int32.fromInt(-_i);
+  int32 operator -() => new int32.fromInt(-_i);
 
   intx operator *(other) {
     if (other is int64) {
       return this.toInt64() * other;
     }
     // TODO(rice) - optimize
     return (this.toInt64() * other).toInt32();
   }
 
   int32 operator %(other) {
@@ skipping 153 matching lines @@
   }
 
   int toInt() => _i;
   int32 toInt32() => this;
   int64 toInt64() => new int64.fromInt(_i);
 
   String toString() => _i.toString();
   String toHexString() => _i.toRadixString(16);
   String toRadixString(int radix) => _i.toRadixString(radix);
 }