file.c: remove unnecessary declaration

* file.c (GetLastError): already defined in windows.h on nowadays
  cygwin, and caused the confliction with the system provided
  definition on cygwin64.  by @kou1okada [Fixes GH-433].

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43583 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ChangeLog

@@ -1,3 +1,9 @@
+Sat Nov  9 00:26:50 2013  Nobuyoshi Nakada  <nobu@ruby-lang.org>
+
+	* file.c (GetLastError): already defined in windows.h on nowadays
+	  cygwin, and caused the confliction with the system provided
+	  definition on cygwin64.  by @kou1okada [Fixes GH-433].
+
 Fri Nov  8 18:35:31 2013  Masaki Matsushita  <glass.saga@gmail.com>
 
 	* lib/open3.rb: receive arguments as keyword arguments.

file.c

@@ -4302,7 +4302,6 @@ rb_file_truncate(VALUE obj, VALUE len)
 
 #ifdef __CYGWIN__
 #include <winerror.h>
-extern unsigned long __attribute__((stdcall)) GetLastError(void);
 #endif
 
 static VALUE