Remove workaround for discord android app users when Discord fixes the underlying issue

[mattyg]

Here is all the info we have about the underlying bug in the discord app that necessitated #302

This ticket is just to keep track of it -- so that if / when the issue is resolved on Discord's android app, we can revert the workaround and notify users that they no longer need to enter another character before the username in receiver: @mentions

there isn't much info on the support page / document about that(https://discord.com/channels/613425648685547541/964289450626650112/964289450626650112). (tbh, discord doesn't do a good job at documenting their bugs)

Most of my info came from some of the devs in the Discord Developers group, that do testing on the latest alpha builds.
Vyvy-vi — Today at 4:05 AM
some convo about the same over here - https://discord.com/channels/613425648685547541/788586647142793246/946504032934060042

On the mention formatting issue -
https://discord.com/developers/docs/reference#message-formatting

previously, there were two kinds of User mentions - <@userid>, which renders as @username

• <@!userId>, which renders as @Nickname

this has been deprecated, and either mention turns to @Nickname, I didn't account for cases when the user's application interprets their mentions as <@userid>