chore: Remove block that disables mocking for tests in the child process

[brannondorsey]

Not for merge right now. I mainly just want to see what MacOS tests will break.

[brannondorsey]

Here are the two tests which fail on MacOS if we re-enable mocking in the child process.

  ---- tests::waitpid_interrupted_by_signal_mock stdout ----
  
  thread 'tests::waitpid_interrupted_by_signal_mock' panicked at src/tests.rs:628:31:
  called `Result::unwrap()` on an `Err` value: CallableStatusUnknown(ChildProcessKilledBySignal(5))
  
  ---- tests::with_mock_helper stdout ----
  
  thread 'tests::with_mock_helper' panicked at src/tests.rs:368:77:
  called `Result::unwrap()` on an `Err` value: CallableStatusUnknown(ChildProcessKilledBySignal(5))
  
  
  failures:
      tests::waitpid_interrupted_by_signal_mock
      tests::with_mock_helper
  
  test result: FAILED. 34 passed; 2 failed; 0 ignored; 0 measured; 0 filtered out; finished in 0.56s