Remove unused ImePreedit component from text_input example (#12818)

# Objective

- The `ImePreedit` component from
[`text_input`](50699ecf76/examples/input/text_input.rs (L126-L127))
appears to be unused.
- This was found by running `cargo check --workspace --examples`,
originally as part of #12817.

## Solution

- Remove it :)

examples/input/text_input.rs

@@ -123,9 +123,6 @@ struct Bubble {
     timer: Timer,
 }
 
-#[derive(Component)]
-struct ImePreedit;
-
 fn bubbling_text(
     mut commands: Commands,
     mut bubbles: Query<(Entity, &mut Transform, &mut Bubble)>,