unprotect(vTree) {
    if (protect.has(vTree) || allocate.has(vTree)) {
      protect.delete(vTree);
      allocate.add(vTree);
    }
  }
Moves a VTree from "protected" state to "allocated" state. They will be
brought back into "free" circulation during a GC.

@param {VTree} vTree - Virtual Tree to unprotect and deallocate