tests: remove unused import

tests: remove unused import

Fixes:

warning: unused import: `with_procspawn_tempdir::with_procspawn_tempdir`
  --> src/test.rs:11:9
   |
11 | pub use with_procspawn_tempdir::with_procspawn_tempdir;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
help: if this is a test module, consider adding a `#[cfg(test)]` to the containing module
  --> src/insttestmain.rs:9:1
   |
9  | mod test;
   | ^^^^^^^^^
   = note: `#[warn(unused_imports)]` on by default