Map the kab_KAB locale to kab for Crowdin sync

Currently Crowdin is syncing the Kabyle language with the language code
kab_KAB. This locale code cannot be detected by gettext, as this tool
detects locale codes that only have 2 characters after the underscore.

This is causing the `gettext:regenerate` command to delete the
`locale/kab_KAB/gitlab.po` file every time it is run.

This change:

1. Update the Crowdin config to map `kab_KAB` to just `kab`
1. Deletes `kab_KAB` locale file (which currently has 0% translation
   anyway).

Issue: https://gitlab.com/gitlab-org/gitlab/-/issues/235511

crowdin.yml

@@ -17,6 +17,7 @@ files:
         fr: fr
         it: it
         ja: ja
+        kab: kab
         ko: ko
         ru: ru
         uk: uk