Fix linter warning in schema

[larry0x]

We get a lot of these when generating JSON schemas:

warning: unused `Result` that must be used
  --> /var/folders/zl/2fy00jl13gv4dvd76h9g8yvr0000gn/T/fsio_dGGCgBbJ5d.rs:56:5
   |
56 |     fs::remove_dir_all("schema");
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: this `Result` may be an `Err` variant, which should be handled
help: use `let _ = ...` to ignore the resulting value
   |
56 |     let _ = fs::remove_dir_all("schema");
   |     +++++++