docs: remove outdated status documents and fix references

- Remove TESTING_SUMMARY.md (describes reverted wit-bindgen-rt implementation)
- Remove VERSION_MANAGEMENT.md (outdated internal analysis, not user-facing)
- Remove WINDOWS_SUPPORT.md (outdated status doc, Windows now works via git_override)
- Remove embedded_runtime_fix.md (describes approach that was reverted)
- Fix clippy.md reference to non-existent scripts/clippy.sh

These were all internal status/analysis docs from development work,
not evergreen user-facing documentation. Keeping only docs that
provide lasting value to users.

Author: avrabe