Remove the 'RUCSS' acronym from the Remove Unused CSS button

[camilamadronero]

This is just a suggestion to clean up the UI, by removing the RUCSS acronym from the Remove Unused CSS button in the File Optimization tab:

If I understand correctly, this acronym is just a "leftover" from the original wording of 3.17 which included RUCSS optimizations.

Thanks!