Review benchmark code

[mervyn-mccreight]

There are some benchmarks defined in kgraphql/src/jmh/kotlin/com/apurebase/kgraphql. Currently they are not really easily executable, nothing is configured in Gradle as far as I can see.

I'd say we should evaluate:

• does the code even work like it is now
• do we want to replace the tooling with https://github.com/Kotlin/kotlinx-benchmark
• do we want to remove the benchmark code at all at the moment