Thanks for that comment! I was bummed that that option is not available as well in typeform. You can’t even have html there. I’re removed the buttons now and added text to suggest folks share the survey with their friends. We want to get as many people who are interested in Discourse to have a chance to give input.
We are going to be sharing the survey ourselves via our social media channels so when you see our posts, please feel very free to share it further! And thank you! 
I also submitted a support request to typeform to allow more control over which social sharing buttons are shown. I could upgrade and link to a page on our own website where we can show whatever we want, but that feels like overkill to me at this stage.