Stop bundling the Twemoji emoji font

[guihkx]

Reasons:

• Upstream doesn't want to provide the font as a TTF file.
• The current TTF file is very outdated (4 years old), so newer emojis aren't supported anyway.
• It doesn't make sense to include any font in the first place: Users can install any emoji font directly on the host, and Flatpak will pick it up automatically for Discord to use.

Closes #334

[flathubbot]

Started test build 151823

[flathubbot]

Build 151823 successful
To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/134906/com.discordapp.Discord.flatpakref

[lionirdeadman]

The reason this was added is because :

1. At the time, people were experiencing issues with Symbola being the preferred emoji on their systems which made some of the UI inconsistent with other platforms (the emojis of Symbola are monochrome and have variable width)
2. Twemoji remains the emoji used on Discord web regardless of platform
3. It provided consistency with the text channels since they always use Discord's own Twemoji

Anyhow, it's probably no longer necessary today. It was my bad for not updating the ttf.

[guihkx]

Thanks for explaining the reasons! I do actually remember getting monochrome emojis back in the day, even though I had noto-emoji-color installed on the host...

If I recall correctly, my solution at the time was to create a custom fontconfig file on the host to prioritize noto-emoji-color, and then I gave all Flatpak apps read-only access to it. It worked well. :p