Revert "net: move context cancellation logic of blocking calls to a common function."

Revert "net: move context cancellation logic of blocking calls to a common function."

This reverts CL 463231.

Reason for revert: introduced a data race on darwin.

Fixes #58169.

Change-Id: I35f02273db38c257369c166547bb4945f92fdc3a
Reviewed-on: https://go-review.googlesource.com/c/go/+/464375
Auto-Submit: Bryan Mills <bcmills@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Ian Lance Taylor <iant@google.com>