"Why don't you remove that old and ancient speech from here?"
Here's a breakdown of the phrase:
* quin: Why not?
* tu: You
* istanc: That (accusative case of "ista")
* orationem: Speech
* hinc: From here
* veterem: Old
* atque: And
* antiquam: Ancient
* amoves: You remove (imperative form of "amovere")
The phrase implies a speaker who is asking someone to stop using outdated or old-fashioned language. It might be used in a rhetorical context to emphasize the importance of using fresh and current language.