Remove unused shader define (#8981)

Unused since #5703

Author: tim-blackbird

crates/bevy_gizmos/src/pipeline_3d.rs

@@ -70,7 +70,6 @@ impl SpecializedRenderPipeline for LineGizmoPipeline {
 
     fn specialize(&self, key: Self::Key) -> RenderPipelineDescriptor {
         let mut shader_defs = vec![
-            "GIZMO_3D".into(),
             #[cfg(feature = "webgl")]
             "SIXTEEN_BYTE_ALIGNMENT".into(),
         ];