test: refactor test-tls-enable-trace-cli.js

This test appears to be flakey on Unix. I'm not entirely sure why, but I think it may be related to the additional piping of the child process stderr (although this test is mostly a copy of another test that isn't exhibiting problems). This commit simplifies the test a bit.

Some preliminary testing seems promising:

• node-test-commit: https://ci.nodejs.org/job/node-test-commit/28351/
• Re-run on Linux, even though no failures were seen on the previous run: https://ci.nodejs.org/job/node-test-commit-linux/27396/
• Stress test: https://ci.nodejs.org/job/node-stress-single-test/2205/

If the stress test comes back green, I'd recommend fast tracking this.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• commit message follows commit guidelines