Remove broken links

Author: DiegoAndai

docs/.link-check-errors.txt

@@ -1,5 +1,2 @@
 Broken links found by `pnpm docs:link-check` that exist:
 
-- https://mui.com/material-ui/customization/theme-components/#creating-new-component-variants
-- https://mui.com/material-ui/customization/theme-components/#overrides-based-on-props
-- https://mui.com/material-ui/react-grid2/#whats-changed

docs/data/material/migration/migration-grid-v2/migration-grid-v2.md

@@ -80,7 +80,7 @@ The Grid v2 is marked as stable in Material UI v6, so the `Unstable_` prefix is
 ```
 
 Alongside the stabilization, the API has been improved.
-You can see the changes and further details on how to migrate in the [Material UI v6 upgrade guide](/material-ui/migration/upgrade-to-v6/#grid-v2-unstable-grid).
+You can see the changes and further details on how to migrate in the [Material UI v6 upgrade guide](/material-ui/migration/upgrade-to-v6/#grid2).
 
 Finally, the original Grid component is deprecated and will be removed in the future, so we highly encourage you to migrate to Grid v2.