test: refactor test-stream-pipe-after-end

• replace process.on('exit', ...) checks with common.mustCall()
• assert.equal() -> assert.strictEqual()
• provide duration of 1ms to timer without a duration
• remove unused function argument

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

test stream