chore(mise/ruby): remove ruby-install backend setting

No longer needed; default ruby-build backend is sufficient.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

config/mise/config.toml

@@ -24,9 +24,6 @@ bun = true
 uvx = true
 
 [settings.ruby]
-# ruby-install supports new releases immediately, as opposed to ruby-build which
-# requires an update before new releases are available.
-ruby_install = true
 # Precompiled binaries causes issues with Ruby LSP.
 compile = true