Remove unused functions reported by cppcheck (#10463)

Run unused functions reported by cppcheck

This change removes a few (but not all) unused functions.
Some unused helper functions were not removed due to their complexity and potential of future use.

src/network/networkpacket.h

@@ -64,7 +64,6 @@ class NetworkPacket
 
 	std::string readLongString();
 
-	char getChar(u32 offset);
 	NetworkPacket &operator>>(char &dst);
 	NetworkPacket &operator<<(char src);