Kick out all the unused logic

...ect/briar/desktop/privategroups/PrivateGroupInfoDrawer.kt

...arproject/briar/desktop/privategroups/PrivateGroupList.kt

.../briar/desktop/privategroups/PrivateGroupListViewModel.kt

...project/briar/desktop/privategroups/PrivateGroupScreen.kt

...briar/desktop/privategroups/ThreadedConversationHeader.kt

...t/briar/desktop/privategroups/ThreadedConversationItem.kt

.../desktop/privategroups/ThreadedConversationMessageItem.kt

...briar/desktop/privategroups/ThreadedConversationScreen.kt

...ar/desktop/privategroups/ThreadedConversationViewModel.kt

.../briarproject/briar/desktop/privategroups/ThreadedText.kt