Add "-rf" for rm to ignore file not found error

Signed-off-by: Aristo Chen <aristo.chen@canonical.com>

snapcraft_legacy/plugins/v2/_kernel_build.py

@@ -1111,7 +1111,7 @@ def _arrange_install_dir_cmd(install_dir: str) -> List[str]:
  # but snapd expects modules/ and firmware/
  mv {install_dir}/lib/modules {install_dir}/
  # remove symlinks modules/*/build and modules/*/source
- rm {install_dir}/modules/*/build {install_dir}/modules/*/source
+ rm -rf {install_dir}/modules/*/build {install_dir}/modules/*/source
  # if there is firmware dir, move it to snap root
  # this could have been from stage packages or from kernel build
  [ -d {install_dir}/lib/firmware ] && mv {install_dir}/lib/firmware {install_dir}