linux: Consolidate internal_statvfs

Remove the internal_statvfs64.c and open code the implementation
on internal_statvfs.c.  The alpha is now unrequired, the generic
implementation also handles it.

Also, remove unused includes on internal_statvfs.c, and remove
unused arguments on __internal_statvfs{64}.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

sysdeps/unix/sysv/linux/statvfs.c

@@ -33,7 +33,7 @@ __statvfs (const char *file, struct statvfs *buf)
     return -1;
 
   /* Convert the result.  */
-  __internal_statvfs (file, buf, &fsbuf, -1);
+  __internal_statvfs (buf, &fsbuf);
 
   /* We signal success if the statfs call succeeded.  */
   return 0;