I was going to ask about this, but figured out a way to do it myself so I’ll post it here since I’m sure this gets asked a lot and I couldn’t find anyone that had an elegant solution.
Add the following to CSS. It will hide all messages that are posted by the username “Chat”, which gets rid of those initial few lines every time you first start it up. Let me know if you find any problems that this might cause.
.chat_line[data-nick='Chat'] {
display: none;
}