Fix supported OS attributes for api.kde.org
Summary:
Move the "maintainer needed" to a note, so it's not showing up globally
for all modules. Also, change "macOS" back to "MacOSX" (despite technically
being the right name), as every other module still uses MacOSX and thus
using anything else essentially adds a new OS on api.kde.org, globally.
Reviewers: Frameworks, apol
Reviewed By: apol
Subscribers: apol, plasma-devel
Tags: Kirigami
Differential Revision: https://phabricator.kde.org/D23188