Relevant magazine has it covered:
It appears that the president of Liberty University has deleted a crude tweet he sent to pastor and author David Platt.
Yesterday, he sent a tweet that read, “Sorry to be crude but pastors like [David Platt] need to grow a pair. Just saying.” That tweet no longer appears on his timeline.
I am guessing there were economic considerations at work here. Falwell must have come to the conclusion that the tweet was not good for Liberty University.