[tftp] Remove configuration option for tftm

DOWNLOAD_PROTO_TFTM is now useless as tftm support has been merged
into tftp.c.  DOWNLOAD_PROTO_TFTP should be used instead.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/config/config.c

 #ifdef DOWNLOAD_PROTO_FTP
 REQUIRE_OBJECT ( ftp );
 #endif
-#ifdef DOWNLOAD_PROTO_TFTM
-REQUIRE_OBJECT ( tftm );
-#endif
 #ifdef DOWNLOAD_PROTO_SLAM
 REQUIRE_OBJECT ( slam );
 #endif

src/config/general.h

 #define	DOWNLOAD_PROTO_HTTP	/* Hypertext Transfer Protocol */
 #undef	DOWNLOAD_PROTO_HTTPS	/* Secure Hypertext Transfer Protocol */
 #undef	DOWNLOAD_PROTO_FTP	/* File Transfer Protocol */
-#undef	DOWNLOAD_PROTO_TFTM	/* Multicast Trivial File Transfer Protocol */
 #undef	DOWNLOAD_PROTO_SLAM	/* Scalable Local Area Multicast */
 
 /*