Use system emoji instead of emojibase

To be honest, emojibase's emojis are absolutely terrible, I hate every single one. My Linux system's emoji font is much nicer-looking and it would be nice if Keybase used system's emoji font instead of emojibase's if configured so.

The issue names no file, test, or entry point; begin by locating the client’s emoji rendering path and its emojibase integration. Determine how a configured Linux system emoji font should be selected, and verify the behavior with and without that configuration.

Written by the indexing model from the issue text.