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

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

The generated constants were already removed by CL 497076, so the cgo
constants used to generate them are no longer needed as well.

Change-Id: I37dabd800461d134424af8bd72fb0c1b8504d604
Reviewed-on: https://go-review.googlesource.com/c/go/+/509676
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Tobias Klauser <tobias.klauser@gmail.com>