Make packet charset configurable

Better support for different language clients such as Thai or Korean

src/main/java/net/packet/Packet.java

@@ -1,10 +1,5 @@
 package net.packet;
 
-import java.nio.charset.Charset;
-import java.nio.charset.StandardCharsets;
-
 public interface Packet {
-    Charset STRING_CHARSET = StandardCharsets.US_ASCII;
-
     byte[] getBytes();
 }