Stop multiplying duration values

Summary:
After D28144, some animations are now too long because they were inappropriately
multiplying a duration value. That's no longer necessary, so let's remove the
multiplication.

Depends on D28144

Test Plan: Various things that were a bit too slow before feel just right now

Reviewers: #vdg, #plasma

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D28239