Text fix: Less -> Fewer options

Summary:
BUG: 344531

Changed "Less Options" button text to "Fewer Options", as is
grammatically correct.

I kept the variable names constant so as to make this a simpler fix,
though that can of course be changed as well.

Reviewers: djarvie, knauss

Reviewed By: knauss

Subscribers: knauss, kde-pim

Tags: #kde_pim

Differential Revision: https://phabricator.kde.org/D19113