test: improve test-fs-empty-readStream.js

Checklist

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

Affected core subsystem(s)

test

Description of change

• use const instead of var
• use common.mustCall to control functions execution
• use assert.strictEqual instead of assert.equal
• use arrow functions