Spurious failure in test_inherit_env

[kennytm]

Symptom: the test process::tests::test_inherit_env failed even if the PR doesn't touch this part of the standard library.

[01:56:52] test process::tests::test_inherit_env ... FAILED
...
[01:56:52] thread '<unnamed>' panicked at 'output doesn't contain `RUN_TEST_NEW_ENV2=456`
...

Previous instances:

• 2018-10-30T10:42:14Z: Update clippy #55496 (comment) (arm-android)
• 2018-09-08T08:22:09Z: Update Cargo and RLS #53935 (comment) (x86_64-gnu-distcheck)

It is known that this test had a race condition, and the fix #42795 wasn't merged.

[Enselic]

This issue can be closed, because the test was removed in d1cd4e8