[gnome-builder/wip/gtk4-port] plugins/cargo: fix warning

[Christian Hergert <chergert src gnome org>]

commit f05b42061dfdeb9c3b7a1922a1af6c9a6650e998
Author: Christian Hergert <chergert redhat com>
Date:   Wed May 25 17:13:40 2022 -0700

    plugins/cargo: fix warning

 src/plugins/cargo/gbp-cargo-build-system.c | 1 -
 1 file changed, 1 deletion(-)
---
diff --git a/src/plugins/cargo/gbp-cargo-build-system.c b/src/plugins/cargo/gbp-cargo-build-system.c
index b281306c4..959036f32 100644
--- a/src/plugins/cargo/gbp-cargo-build-system.c
+++ b/src/plugins/cargo/gbp-cargo-build-system.c
@@ -220,7 +220,6 @@ gbp_cargo_build_system_locate_cargo (GbpCargoBuildSystem *self,
                                      IdeConfig           *config)
 {
   g_autofree char *cargo_in_home = NULL;
-  IdeRuntime *runtime = NULL;
   const char *envvar;
 
   g_return_val_if_fail (!self || GBP_IS_CARGO_BUILD_SYSTEM (self), NULL);