Remove a duplicate declaration

This is already declared in sys/file.h, which is included directly.
Compiling with GCC9 emits an error.

Discussed with: rmacklem

sys/rpc/rpcsec_tls/rpctls_impl.c

@@ -62,8 +62,6 @@ __FBSDID("$FreeBSD$");
 #include "rpctlscd.h"
 #include "rpctlssd.h"
 
-extern struct fileops badfileops;
-
 /*
  * Syscall hooks
  */