Remove mkdirp

[jakebailey]

If our build scripts target Node 10+, we can use the builtin mkdir
function in recursive mode instead.

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Please do not comment on this PR. Depending on how this set of PRs evolves, this PR's contents may change entirely based on the order of commits.

This PR is a part of a stack:

1. Make a few changes to allow all code to be loaded as one project
2. Explicitly reference ts namespace in tsserverlibrary
3. Generated module conversion step - unindent
4. Generated module conversion step - explicitify
5. Generated module conversion step - stripNamespaces
6. Generated module conversion step - inlineImports
7. Generated module conversion step - .git-ignore-blame-revs
8. Add gitlens settings suggestion
9. Make processDiagnosticMessages generate a module
10. Fix up linting, make lint clean
11. Undo changes needed to load codebase into ts-morph
12. Add JSDoc eslint rule
13. Fix all internal JSDoc comments
14. Convert require calls to imports
15. Remove typescriptServices, protocol.d.ts, typescript_standalone.d.ts
16. Get codebase building pre bundling
17. Add build via esbuild
18. Add dts bundling
19. Consolidate checks that test if the current environment is Node
20. Add ts to globalThis in run.js for convenience during debugging
21. Rename Gulpfile to Herebyfile for improved git diff
22. Change build system to hereby
23. Update baselines for corrected line endings in lib files
24. Use jsonc-parser instead of LKG compiler in build
25. Modernize localize script, use new XML library
26. Don't use needsUpdate for quick tasks
27. Remove mkdirp (this PR)
28. Export ts namespace from tsserver for hacky-post patching
29. Directly import namespaces for improved esbuild output
30. Ensure ts object passed to plugins contains deprecatedCompat declarations
31. Move compiler-debug into Debug namespace, which allows the compiler to be tree shaken
32. Remove Promise redeclaration
33. Remove globalThisShim and globalThis modification for TypeScriptServicesFactory
34. Disable slow CodeQL queries
35. Remove outFiles from launch.json
36. Remove dynamicImport and setDynamicImport