Why will there be no more false visions?
Rashi: The false Nevi'im will not be able to falsely promise to you Shalom, for the true Nevi'im's words will come soon.
Radak: The land will be desolate. Their visions will be Batel, and the false Nevi'im will perish.
What is "Miksam Chalak"?
Rashi: It is divination of flattery.
Radak #1: There is a Patach under the Samech, for it is not Samuch. Chalak is an adjective. If it were a noun, it would be Samuch, like Chazon Shav.
Radak #2: Miksam is Samuch. Chalak is a To'ar ? a kind of man who speaks flattery, i.e. a false Navi. Miksam and Kesem encompass matters done to know the future.
Malbim: Kesem is via Chachamim of nature; they flatter people. Chazon is what is seen in the stars.