pre-commit: remove markdown-link-check hook

External link checkers are inherently flaky in CI due to
websites blocking automated requests (e.g. 403 errors).
Also remove JSON hooks (pretty-format-json, check-json)
since no JSON files remain in the repository.

Co-authored-by: Claude <noreply@anthropic.com>

.github/linters/mlc_config.json

@@ -1,26 +0,0 @@
-{
-  "retryOn429": true,
-  "retryCount": 3,
-  "aliveStatusCodes": [
-    200,
-    206,
-    502
-  ],
-  "ignorePatterns": [
-    {
-      "pattern": "^https://github.com/mruby/mruby/commit/"
-    },
-    {
-      "pattern": "^http://jp.rubyist.net/magazine/\\?0034-Enumerable_lz"
-    },
-    {
-      "pattern": "^https://ruby-doc.org/core-2.3.3"
-    },
-    {
-      "pattern": "^mailto:"
-    },
-    {
-      "pattern": "^https://www.iso.org/"
-    }
-  ]
-}