Move gpui derives tests into gpui crate to avoid dependency cycles

`cargo run` on Zed project leads to rust-analyzer evantually emitting

`[ERROR project_model::workspace] cyclic deps:
gpui_macros(Idx::<CrateData>(269)) -> gpui(Idx::<CrateData>(264)),
alternative path: gpui(Idx::<CrateData>(264)) ->
gpui_macros(Idx::<CrateData>(269))`

error after loading the project.

The PR fixes this by moving away the test to the "root" project.

crates/gpui_macros/Cargo.toml

@@ -13,6 +13,3 @@ doctest = false
 syn = "1.0"
 quote = "1.0"
 proc-macro2 = "1.0"
-
-[dev-dependencies]
-gpui = { path = "../gpui" }

crates/gpui_macros/tests/test.rs

@@ -1,14 +0,0 @@
-use gpui::{elements::RenderElement, View, ViewContext};
-use gpui_macros::Element;
-
-#[test]
-fn test_derive_render_element() {
-    #[derive(Element)]
-    struct TestElement {}
-
-    impl RenderElement for TestElement {
-        fn render<V: View>(&mut self, _: &mut V, _: &mut ViewContext<V>) -> gpui::AnyElement<V> {
-            unimplemented!()
-        }
-    }
-}