tool_customlang CLI export leaves empty directory

Steps to reproduce:

• In your Moodle instance, customize some language strings of the english language pack within the language customization GUI.
• Open your terminal and run this command:

  php admin/tool/customlang/cli/export.php --lang=en --target=/tmp/en_local

Expected result:

• There should be a zip file at /tmp/en_local.zip
• There shouldn't be any other leftovers from the export within /tmp

Actual result:

• There is a zip file at /tmp/en_local[[exportzipfilename]] (which is a bug reported at MDL-75970, just to be precise here)
• There is an empty leftover directory at /tmp/en_local

Analysis:

• The CLI export seems to copy the customized language pack files first and zip them afterwards. However, it misses to remove the customized language pack files at the end and keep only the zip file.