Don't attempt to strip markup from a KNotification's title

The KNotification documentation mentions that the text property can contain markup, but makes no such claim for title, implying that the latter is plaintext.

This parallels the Desktop Notifications Specification, which states that "Body text may contain markup"¹ without a similar mention for the summary/title. Although not stated explicitly, this has been widely accepted as indicating that the summary is indeed plaintext (and Plasma handles it as such²³).

Consequently, we should not attempt to strip any markup from the title; users can rightfully expect that a string like a<b&b>a will not get mangled in the process.

This commit removes all calls to stripRichText(title), namely in the Popup, Android and Snore plugins.

As for the MacOS and Portal plugins, although the absence of any such call might lead one to assume that a string with markup was expected before (which would now require some characters to be escaped), their respective documentation⁴⁵ implies the opposite, so no action was taken.

1. https://specifications.freedesktop.org/notification-spec/latest/ar01s04.html#markup
2. https://github.com/KDE/plasma-workspace/blob/d3adf06c72301365b0c707f968974574e345adac/dataengines/notifications/notificationsengine.cpp#L86-L87
3. https://github.com/KDE/plasma-workspace/blob/a5c7df39460eff7454f992a2307753bfb1eb095f/libnotificationmanager/notification.cpp#L510-L529
4. https://developer.apple.com/documentation/foundation/nsusernotification/1415172-title
5. https://flatpak.github.io/xdg-desktop-portal/portal-docs.html#gdbus-method-org-freedesktop-portal-Notification.AddNotification