Cygwin: drop stray fs_info::check_ssd declaration

This is just a leftover from development

Fixes: 8b01c5d690 ("Cygwin: fs_info: check for SSD")
Signed-off-by: Corinna Vinschen <corinna@vinschen.de>

winsup/cygwin/local_includes/mount.h

@@ -81,8 +81,6 @@ class fs_info
   ULONG sernum;			/* Volume Serial Number */
   char fsn[80];			/* Windows filesystem name */
 
-  void check_ssd (HANDLE);
-
  public:
   void clear ()
   {