I'll take a run at that.
There's no provision for that in the Washington treaty. A country could in theory elect to leave, provide notice and so on, but there's no provision for other members of NATO to remove a country from the alliance.
With regard to Turkey, if I might, there is a current concern, and there has been for a number of years, in light of what's going on in Syria. The Turks have said on occasion that they would like to create a buffer zone inside Syria in order to protect their country. Other NATO allies have provided warnings in a sense, a yellow light to the Turks, which is that if their entanglement across the border leads to an attack on their territory from abroad, that's an article 5 event, and we would just as soon not become involved in their adventures. They wouldn't put it that way, but that's essentially what they'd mean.
There has already been a discussion with regard to one specific ally as to how their behaviour outside their borders could entangle NATO in a conflict in which it does not wish to become involved. This is, in a sense, heading down this path, which is why allies can call for a consultation on any specific issue. There have been consultations of this kind in the past. That's not removal of an ally; that's a sign from other allies that we are concerned about a specific military operation.