runtime: remove map stack version handling for openbsd
OpenBSD 6.3 is more than five years old and has not been supported for
the last four years (only 7.3 and 7.4 are currently supported). As such,
remove special handling of MAP_STACK for 6.3 and earlier.
Change-Id: I1086c910bbcade7fb3938bb1226813212794b587
Reviewed-on: https://go-review.googlesource.com/c/go/+/538458 Reviewed-by: Cherry Mui <cherryyz@google.com> Reviewed-by: Bryan Mills <bcmills@google.com> Reviewed-by: Aaron Bieber <aaron@bolddaemon.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Joel Sing <joel@sing.id.au>