get rid of old ContactsActivity

[mahibi]

It seems that the old ContactsActivity is still exisiting next to ContactsActivityCompose. It's in use in ConversationInfoActivity to add more participants.

• ContactsActivity should either be deleted and replaced by ContactsActivityCompose which must be able to handle the use case. or
• code that is not used anymore in ContactsActivity should be deleted and the class should be renamed.

After all, ContactsActivityCompose should be renamed to ContactsActivity.

Nothing for 20.0.0, it should be done afterwards..