The docs/hooks.txt file described the hook system from MediaWiki
1.34 and earlier. Its continued presence was confusing to developers,
who were not sure if they should update it. Remove the majority of
this file and direct developers to Hooks.md, which describes the
hook system implemented in 1.35. Also add a link to
https://www.mediawiki.org/wiki/Manual:Hooks to both hooks.txt and
Hooks.md.
Bug: T257804
Change-Id: I5998f179acde1a7fb1053c23305f949fa63542d9
Add a "silent" flag to DeprecatedHooks which causes relevant deprecation
warnings to be suppressed, but still allows call filtering to be used.
Add existing hooks that are documented as deprecated to the array.
Change-Id: Ieeb5e1840fd06d2b7979ef7827ba82bd2a35a2ba
