configure: Remove unused variable default_cflags
configure has a variable default_cflags, which was originally added in commit bafe78ad3bc4c ("contrib/plugins: use an independent makefile") as part of it setting up the build environment for contrib/plugins, which at the time used make. However, we now build the plugins with meson, and in commit 55c84a72aba4 ("contrib/plugins: remove Makefile for contrib/plugins") we dropped the logic from configure that does that makefile setup, leaving default_cflags as an unused variable. shellcheck helpfully reports this: default_cflags='-O0 -g' ^------------^ SC2034 (warning): default_cflags appears unused. Verify use (or export if used externally). Remove the unused variable. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org> Message-id: 20260317120215.2075164-1-peter.maydell@linaro.org