No, the ideal of free speech is that you should get to express yourself, and I should get to express myself. Through discussion we may gain common understanding and benefit. We can discover unfamiliar perspectives, debate ideas, and figure out meaningful truths. We both will also appreciate the opportunity to have our thoughts heard - whatever they may be.

Stopping speech because you dislike the speaker, or disagree with what's being said is the antithesis of this ideal.

Again, of course Twitter legally could ban Trump. Doing so would not be in keeping with the ideal of free speech.