udhcpc: revert deprecation message for -V

"-x vendor:VENDOR" will not be a trivial replacement of it:

(1) by default, we do send a vendor string ("udhcp BB_VER"),
will need code to preserve the default.

(2) -V '' currently disables vendor string. -x vendor:''
would not easily achieve that: it adds no option at all
(string options can't be empty), and default (1) would trigger.
To avoid that, we will need yet another hack to detect
-x vendor:'' and interpret that as "no vendor string at all".

IOW: removing -V is likely to increase code size, not decrease.

function                                             old     new   delta
udhcpc_main                                         2563    2555      -8
.rodata                                           103251  103198     -53
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-61)             Total: -61 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

networking/udhcp/dhcpc.c

@@ -1326,10 +1326,7 @@ int udhcpc_main(int argc UNUSED_PARAM, char **argv)
 	}
 	if (str_V[0] != '\0') {
 		char *p;
-		unsigned len;
-		//msg added 2021-06
-		bb_error_msg("option -V VENDOR is deprecated, use -x vendor:VENDOR");
-		len = strlen(str_V);
+		unsigned len = strnlen(str_V, 254);
 		p = udhcp_insert_new_option(
 				&client_data.options, DHCP_VENDOR,
 				len, /*dhcp6:*/ 0);