[applet] Remove unnecessary top margin

Summary:
This top margin is unnecessary; see D28089 for more details.

Depends on D28089

Test Plan:
Before: {F8180323}
After: {F8180322}

Reviewers: #vdg, #plasma, dantti, ndavis

Reviewed By: #vdg, ndavis

Subscribers: kde-utils-devel

Differential Revision: https://phabricator.kde.org/D28091