message: Remove `PaneGrid::split_*` helpers
  We can use the `split` method directly instead.
diff: @@ -98,18 +98,6 @@ impl<T> State<T> {
  self.internal.focus(pane);
  }
  - pub fn split_vertically(&mut self, pane: &Pane, state: T) -> Option<Pane> {
  - self.split(Axis::Vertical, pane, state)
  - }
  -
  - pub fn split_horizontally(
  - &mut self,
  - pane: &Pane,
  - state: T,
  - ) -> Option<Pane> {
  - self.split(Axis::Horizontal, pane, state)
  - }
  -
  pub fn split(&mut self, axis: Axis, pane: &Pane, state: T) -> Option<Pane> {
  let node = self.internal.layout.find(pane)?;
  