[docs] Remove none generated files

[alexfauquette]

I remove api files, and run pnpm docs:api to see which files are not generated anymore, an so spot pages that are or will be outdated

@cherniavskii For the grid, it's just 2 json without there respective pages to render them

[mui-bot]

Deploy preview: https://deploy-preview-21886--material-ui-x.netlify.app/

Bundle size report

Bundle	Parsed size	Gzip size
@mui/x-data-grid	0B(0.00%)	0B(0.00%)
@mui/x-data-grid-pro	0B(0.00%)	0B(0.00%)
@mui/x-data-grid-premium	0B(0.00%)	0B(0.00%)
@mui/x-charts	0B(0.00%)	0B(0.00%)
@mui/x-charts-pro	0B(0.00%)	0B(0.00%)
@mui/x-charts-premium	0B(0.00%)	0B(0.00%)
@mui/x-date-pickers	0B(0.00%)	0B(0.00%)
@mui/x-date-pickers-pro	0B(0.00%)	0B(0.00%)
@mui/x-tree-view	0B(0.00%)	0B(0.00%)
@mui/x-tree-view-pro	0B(0.00%)	0B(0.00%)

Details of bundle changes

Generated by 🚫 dangerJS against b7bbd73

[codspeed-hq]

Merging this PR will not alter performance

✅ 14 untouched benchmarks

---

_{Comparing alexfauquette:remove-old-pages (b7bbd73) with master (e1d56fa)¹}

Footnotes

1. No successful run was found on master (3fede28) during the generation of this report, so e1d56fa was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩