Remove references to Squashatons

* explainer doc
* reference in community page, including defunct bot

closes #4066

Author: coke

CONTRIBUTING.md

@@ -49,8 +49,6 @@ in the [#raku IRC channel](https://raku.org/community/irc).
 * Be explicit about routine signatures. If a method accepts an `*%args`,
   but treats some of them specially, list them separately.
 * Check out [the styleguide](writing-docs/STYLEGUIDE.md) for further guidance.
-* If you are participating in one of the monthly squashathons,
-  [please read this guide](writing-docs/SQUASHATHONS.md).
 
 ## Documenting versions
 

doc/Language/community.pod6

@@ -203,16 +203,6 @@ B<SourceBaby> (L<details|https://github.com/zoffixznet/perl6-sourceable>)
 Core source code locator
 =end item
 
-=begin item
-B<squashable> (L<details|https://github.com/Raku/whateverable/wiki/Squashable>)
-
-An IRC bot for the Monthly Bug Squash Day (a.k.a. Community Bug
-SQUASHathon). It can be addressed by its full name ('squashable6')
-or its short name ('squash'). It can tell you when the next even is
-going to happen and what's the current status of the active event.
-Also, it will also announce changes to the repo.
-=end item
-
 =begin item
 B<statisfiable> (L<details|https://github.com/Raku/whateverable/wiki/Statisfiable>)