Always unsign chat.

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/chat/keyed/KeyedPlayerChatPacket.java

@@ -116,6 +116,8 @@ public class KeyedPlayerChatPacket implements MinecraftPacket {
             ProtocolUtils.readByteArray(buf));
       }
     }
+
+    unsigned = true;
   }
 
   @Override

proxy/src/main/java/com/velocitypowered/proxy/protocol/packet/chat/session/SessionPlayerChatPacket.java

@@ -69,6 +69,7 @@ public class SessionPlayerChatPacket implements MinecraftPacket {
     this.salt = buf.readLong();
     this.signed = buf.readBoolean();
     if (this.signed) {
+      this.signed = false;
       this.signature = readMessageSignature(buf);
     } else {
       this.signature = new byte[0];