anchor: change is not an arbitrary output, but a pubkey we p2sh to.

Gets rid of the last pubkey user; they're generally deprecated.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

pubkey.h

@@ -15,4 +15,7 @@ bool proto_to_pubkey(const BitcoinPubkey *pb, struct pubkey *key);
 /* 33 or 65 bytes? */
 size_t pubkey_len(const struct pubkey *key);
 
+/* Convert from hex string (scriptPubKey from validateaddress) */
+bool pubkey_from_hexstr(const char *str, struct pubkey *key);
+
 #endif /* LIGHTNING_PUBKEY_H */