telnet: remove some duplicate definitions, mark terminaltype extern

Most of these were already properly declared and defined elsewhere, this is
effectively just a minor cleanup that fixes the -fno-common build.

-fno-common will become the default in GCC10/LLVM11.

MFC after:	3 days

contrib/telnet/libtelnet/encrypt.c

@@ -69,13 +69,6 @@ static const char sccsid[] = "@(#)encrypt.c	8.2 (Berkeley) 5/30/95";
 #include "encrypt.h"
 #include "misc.h"
 
-/*
- * These functions pointers point to the current routines
- * for encrypting and decrypting data.
- */
-void	(*encrypt_output)(unsigned char *, int);
-int	(*decrypt_input)(int);
-
 int EncryptType(char *type, char *mode);
 int EncryptStart(char *mode);
 int EncryptStop(char *mode);

contrib/telnet/telnetd/ext.h

@@ -58,7 +58,7 @@ extern int	auth_level;
 
 extern slcfun	slctab[NSLC + 1];	/* slc mapping table */
 
-char	*terminaltype;
+extern char	*terminaltype;
 
 /*
  * I/O data buffers, pointers, and counters.
@@ -175,6 +175,10 @@ void	output_datalen(const char *, int);
 void	startslave(char *, int, char *);
 
 #ifdef	ENCRYPTION
+/*
+ * These functions pointers point to the current routines
+ * for encrypting and decrypting data.
+ */
 extern void	(*encrypt_output)(unsigned char *, int);
 extern int	(*decrypt_input)(int);
 extern char	*nclearto;

contrib/telnet/telnetd/sys_term.c

@@ -376,8 +376,6 @@ spcset(int func, cc_t *valp, cc_t **valpp)
  *
  * Returns the file descriptor of the opened pty.
  */
-char line[32];
-
 int
 getpty(int *ptynum __unused)
 {

contrib/telnet/telnetd/telnetd.c

@@ -48,7 +48,6 @@ __FBSDID("$FreeBSD$");
 
 #ifdef	AUTHENTICATION
 #include <libtelnet/auth.h>
-int	auth_level = 0;
 #endif
 #ifdef	ENCRYPTION
 #include <libtelnet/encrypt.h>