syscall: do not change stdio handle inheritance

Before the CL 288297 all Go process handles had to be made
non-inheritable - otherwise they would escape into the child process.
But now this is not necessary.

This CL stops changing inheritance flag of stdint, stdout and stderr
handles.

Fixes #44876

Change-Id: Ib8fcf8066c30282293d96c34486b01b4c04f7116
Reviewed-on: https://go-review.googlesource.com/c/go/+/316269


Trust: Alex Brainman <alex.brainman@gmail.com>
Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Run-TryBot: Alex Brainman <alex.brainman@gmail.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Jason A. Donenfeld <Jason@zx2c4.com>