code review 148370043: os, syscall: add Unsetenv

src/syscall/env_windows.go

 // Copyright 2010 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.
 
 // Windows environment variables.
 
 package syscall
 
 import (
         "unicode/utf16"
@@ skipping 70 matching lines @@
                         // empty string marks the end
                         if i <= from {
                                 break
                         }
                         r = append(r, string(utf16.Decode(p[from:i])))
                         from = i + 1
                 }
         }
         return r
 }