gossipd: drop zlib support.

This was removed from the spec on Apr 25, 2022.  We stopped ever sending them
in 0.12.0 (2022-08-23).  Now we remove receive support.

Changelog-Protocol: Removed support for zlib-compressed short-channel-ids in query responses.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

devtools/mkencoded.c

@@ -5,7 +5,6 @@
 #include <ccan/str/hex/hex.h>
 #include <common/decode_array.h>
 #include <stdio.h>
-#include <zlib.h>
 
 static NORETURN void usage(void)
 {
@@ -43,20 +42,7 @@ int main(int argc, char *argv[])
 	if (encoding == ARR_UNCOMPRESSED)
 		printf("%02x%s\n", encoding, tal_hex(NULL, data));
 	else if (encoding == ARR_ZLIB_DEPRECATED) {
-		/* https://www.zlib.net/zlib_tech.html:
-		 *   the only expansion is an overhead of five bytes per 16 KB
-		 *   block (about 0.03%), plus a one-time overhead of six bytes
-		 *   for the entire stream.
-		 */
-		unsigned long compressed_len = tal_bytelen(data)
-			+ 6 + 5*(tal_bytelen(data) + 16384)/16384;
-		u8 *z = tal_arr(NULL, u8, compressed_len);
-		if (compress2(z, &compressed_len, data, tal_bytelen(data),
-			      Z_DEFAULT_COMPRESSION) != Z_OK)
-			errx(1, "Error compressing stream?");
-
-		printf("%02x%s\n", encoding,
-		       tal_hexstr(NULL, z, compressed_len));
+		errx(1, "ZLIB compression deprecated");
 	} else {
 		errx(1, "Unknown encoding %u", encoding);
 	}