CI: update git configuration

- git: clone with depth=1
- git: no recursive submodule
  no more dependency on savannah.nongnu.org nor bearssl.org

package/build_boards_manager_package.sh

@@ -48,15 +48,6 @@ srcdir=$PWD
 rm -rf package/versions/$ver
 mkdir -p $outdir
 
-# Get submodules
-modules=libraries/SoftwareSerial
-for mod in $modules; do
-    echo "refreshing submodule: $mod"
-    git submodule update --init -- $mod
-    (cd $mod && git reset --hard)
-done
-echo "done with submodules"
-
 # Some files should be excluded from the package
 cat << EOF > exclude.txt
 .git