runtime: remove unused _F_{GET,SET}FL constants on solaris and openbsd

runtime: remove unused _F_{GET,SET}FL constants on solaris and openbsd

These are only needed on aix and darwin.

Change-Id: Iea67e4631197359f2bec346ef7d7b723ca23646e
Reviewed-on: https://go-review.googlesource.com/c/go/+/497076
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gopher Robot <gobot@golang.org>