"Platforms" section is very outdated

[jyn514]

https://forge.rust-lang.org/platforms/index.html

off the top of my head:

• @rustlang is no longer active (and twitter probably shouldn't be first in the list of platforms anyway)
• @ruststatus and @rustasync are both dead
• the discord is no longer used by anyone except rustup (and maybe rustfmt, i don't recall).
• i highly doubt that our email is still hosted by mozilla.
• zulip should be listed first

[apiraino]

The Xitter account posted on Apr, 5th that we will no longer post there. We could talk to the social media person and see if we could just close it for good. It's not even on the project website footer anymore.

(FWIW The Foundation is going to dismiss their xitter account(s) as well)