cmdlib: fold commit_ostree_layer into commit_overlay

It's the only caller now, so let's just fold it in so that future code
isn't tempted to use it.

(cherry picked from commit 2ec70d8)

src/cmdlib.sh

@@ -277,14 +277,6 @@ prepare_build() {
     export overrides_active_stamp
 }
 
-commit_ostree_layer() {
-    local rootfs=$1; shift
-    local branch=$1; shift
-    ostree commit --repo="${tmprepo}" --tree=dir="${rootfs}" -b "${branch}" \
-        --owner-uid 0 --owner-gid 0 --no-xattrs --no-bindings --parent=none \
-        --mode-ro-executables --timestamp "${git_timestamp}" "$@"
-}
-
 commit_overlay() {
     local name path respath
     name=$1
@@ -300,7 +292,10 @@ commit_overlay() {
     # files, but we do.
     touch "${TMPDIR}/overlay/statoverride"
     echo -n "Committing ${name}: ${path} ... "
-    commit_ostree_layer "${TMPDIR}/overlay" "overlay/${name}" \
+    ostree commit --repo="${tmprepo}" \
+        --tree=dir="${TMPDIR}/overlay" -b "overlay/${name}" \
+        --owner-uid 0 --owner-gid 0 --no-xattrs --no-bindings --parent=none \
+        --mode-ro-executables --timestamp "${git_timestamp}" \
         --statoverride <(sed -e '/^#/d' "${TMPDIR}/overlay/statoverride") \
         --skip-list <(echo /statoverride)
 }