chore(pre-commit/update-deprecated-links): exclude untracked files

The pre-commit script `update-deprecated-links` creates dangling links
to untracked files (such as the text editor's backup files, the
manually backed up files, some files that will be added later, etc.).
These dangling links would block creating the commit.

In this patch, we check if the target path is tracked by git or not
before creating the symbolic link.

We also would not try to remove untracked files or regular files in
`test/deprecated/completions/`.  We would only remove tracked links.

Author: akinomyoga

test/deprecated/update-deprecated-links

@@ -1,14 +1,20 @@
 #!/bin/bash
 set -euo pipefail
 
+is_tracked_by_git()
+{
+    git ls-files --error-unmatch "$1" &>/dev/null
+}
+
 cd "$(dirname "$0")/completions"
 for f in *; do
-    case $f in
-        Makefile* | README.md) ;;
-        *) git rm -f $f ;;
-    esac
+    if [[ -h $f ]] && is_tracked_by_git "$f"; then
+        git rm -f "$f"
+    fi
 done
 for f in ../../../completions/_*; do
-    ln -sf $f ${f##*/_}
-    git add --verbose ${f##*/_}
+    if is_tracked_by_git "$f"; then
+        ln -sf $f ${f##*/_}
+        git add --verbose ${f##*/_}
+    fi
 done