Small fixes

[emaia]

Changes:

• Removed unused icon images no longer needed since WP 4.3 (missed in remove favicon #784).
• Corrected typo in comment FontAwesome comment.
• Changed img to images in gulp watch task path in gulpfile.babel.js (Missed in Tiny update gulpfile.babel.js #1155).
• Removed unnecessary echoes in front of the_post_thumbnail_url function.
• Removed unnecessary/invalid fourth parameter in remove_action calls in library/cleanup.php.

[colin-marshall]

@emaia congratulations on your first FoundationPress contribution(s)! All look good to me.

For future reference, please add a description to your pull requests outlining the changes. I did it for you on this one.

Thanks for the PR!

[emaia]

@colin-marshall I'm happy to contribute with the FP. Thanks for add a description. I will do this in the next PR.

[olefredrik]

Looks good 👌 Thanks, @emaia and @colin-marshall !