Remove TestInotifyNoBlockingSyscalls (#532)

Remove TestInotifyNoBlockingSyscalls (#532)

This test checks if no additional OS threads are created; this was added
after the old epoll-based inotify code was removed (which would create
additional threads). It's always been a bit flaky: it currently already
runs the test twice and "fails" only if both fail.

We don't really control the Go scheduler and when it creates/destroys OS
threads, or have all that much insight in it (the "threadcreate" profile
in pprof has been broken for years). I tried to make this test a bit
more reliable a few months ago, and the run-it-twice "solution" was the
best I could come up.

It still causes some failures though; see the links below. I don't know
why it consistently fails on armle (and not e.g. arm64), but that seems
a Go thing, rather than a fsnotify thing.

I'm not sure if this test adds all that much value; I don't really
foresee a regression where we accidentally create more OS threads than
we should.

Fixes #531
Also see: https://bugs.launchpad.net/ubuntu/+source/golang-fsnotify/+bug/1971967