Remove MessageItem
Remove MessageItem

Now that it's been replaced by KTp::Message in the only class it
was used, it can safely be removed.

leonhandreke/ktp-common-internals,leonhandreke/ktp-common-internals,KDE/ktp-common-internals,KDE/ktp-common-internals,leonhandreke/ktp-common-internals,KDE/ktp-common-internals