Bug Report

Describe the current, buggy behavior

After running wp core download --skip-content the tinymce editor is broken due to missing plugins & themes directories

Describe how other contributors can replicate this bug

• run wp-core download --skip-content
• attempt to edit content using the TinyMCE editor
• the editor is unresponsive & console shows a 404 for js files
• inspecting the wp-includes/js/tinymce directory shows the plugins & themes directories are both missing

Describe what you would expect as the correct outcome

wp core download --skip-content should only remove the plugins & themes directories in the wp-content directory

Let us know what environment you are running this on

WP-CLI version:	2.7.0

Provide a possible solution

Add an additional check to only remove plugins & themes from the wp-content directory

Provide additional context/Screenshots

Bug appears to have been introduced in #212