salsa-ci: don't change submodule strategy

We don't use submodules for this package.

Signed-off-by: Arnaud Ferraris <arnaud.ferraris@collabora.com>

debian/salsa-ci.yml

 ---
-variables:
-  GIT_SUBMODULE_STRATEGY: recursive
-
 include:
   - https://salsa.debian.org/salsa-ci-team/pipeline/raw/master/salsa-ci.yml
   - https://salsa.debian.org/salsa-ci-team/pipeline/raw/master/pipeline-jobs.yml