* Affected components: MediaWiki core's Composer helper for installing/updating of extensions.
* Engineer(s) or team for initial implementation: TBD.
* Code steward: TBD.
### Motivation
In T467 it was decided not to officially support managing enablement of, or dependencies between, extensions via Composer. This is handled by ExtensionRegistry nowadays.
We should remove the half "support" still existing for those use cases from MediaWiki. Thus removing the expectation that people should be able to install MW or extensions via Composer, even though it's not offically supported.
Pages like https://www.mediawiki.org/wiki/Composer/For_extensions do not help the situation.
### Proposal
* Remove the `pre-install-cmd` and `pre-update-cmd` hooks from MediaWiki's composer.json, which are currently used to provide a composer-requirable "MediaWiki" version.
* Deprecate and remove the then-unused `MediaWikiVersionFetcher` class.
https://gerrit.wikimedia.org/r/#/c/mediawiki/core/+/551346/ was created to do this
See also {T243297} for removing `composer/installers` from extension/skin composer.json files
See also {T250406} which is proposing to properly establish composer based extension management.