Remove useless Direction field (#14793)

# Objective

Delete some code that isn't actually doing anything. This was actually
discovered way back in this obsolete PR: #5513.

Also Fixes #6286

## Solution

Delete it

## Alternatives

Make `Direction` do things. But it's not totally clear to me if it's
possible to override cosmic-text's unicode bidi stuff.

## Migration Guide

`Style` no longer has a `direction` field, and `Direction` has been
deleted. They didn't do anything, so you can delete any references to
them as well.

crates/bevy_ui/src/layout/convert.rs

@@ -454,7 +454,6 @@ mod tests {
             right: Val::Percent(50.),
             top: Val::Px(12.),
             bottom: Val::Auto,
-            direction: crate::Direction::Inherit,
             flex_direction: FlexDirection::ColumnReverse,
             flex_wrap: FlexWrap::WrapReverse,
             align_items: AlignItems::Baseline,

crates/bevy_ui/src/ui_node.rs

@@ -173,13 +173,6 @@ pub struct Style {
     /// <https://developer.mozilla.org/en-US/docs/Web/CSS/overflow>
     pub overflow: Overflow,
 
-    /// Defines the text direction. For example, English is written LTR (left-to-right) while Arabic is written RTL (right-to-left).
-    ///
-    /// Note: the corresponding CSS property also affects box layout order, but this isn't yet implemented in Bevy.
-    ///
-    /// <https://developer.mozilla.org/en-US/docs/Web/CSS/direction>
-    pub direction: Direction,
-
     /// The horizontal position of the left edge of the node.
     ///  - For relatively positioned nodes, this is relative to the node's position as computed during regular layout.
     ///  - For absolutely positioned nodes, this is relative to the *parent* node's bounding box.
@@ -435,7 +428,6 @@ impl Style {
         right: Val::Auto,
         top: Val::Auto,
         bottom: Val::Auto,
-        direction: Direction::DEFAULT,
         flex_direction: FlexDirection::DEFAULT,
         flex_wrap: FlexWrap::DEFAULT,
         align_items: AlignItems::DEFAULT,
@@ -730,35 +722,6 @@ impl Default for JustifyContent {
     }
 }
 
-/// Defines the text direction.
-///
-/// For example, English is written LTR (left-to-right) while Arabic is written RTL (right-to-left).
-#[derive(Copy, Clone, PartialEq, Eq, Debug, Reflect)]
-#[reflect(Default, PartialEq)]
-#[cfg_attr(
-    feature = "serialize",
-    derive(serde::Serialize, serde::Deserialize),
-    reflect(Serialize, Deserialize)
-)]
-pub enum Direction {
-    /// Inherit from parent node.
-    Inherit,
-    /// Text is written left to right.
-    LeftToRight,
-    /// Text is written right to left.
-    RightToLeft,
-}
-
-impl Direction {
-    pub const DEFAULT: Self = Self::Inherit;
-}
-
-impl Default for Direction {
-    fn default() -> Self {
-        Self::DEFAULT
-    }
-}
-
 /// Defines the layout model used by this node.
 ///
 /// Part of the [`Style`] component.