cmd/go/internal/script: remove special-case escaping logic for $WORK

cmd/go/internal/script: remove special-case escaping logic for $WORK

Previously, the script engine implicitly escaped the path in the
$WORK environment variable to be the literal string '$WORK', which
produces somewhat better error messages in case of failure.

However, for a general-purpose script engine that implicit behavior is
surprising, and it isn't really necessary.

For #27494.

Change-Id: Ic1d5b8801bbd068157315685539e7cc2795b3aa5
Reviewed-on: https://go-review.googlesource.com/c/go/+/426854
Reviewed-by: Russ Cox <rsc@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Run-TryBot: Bryan Mills <bcmills@google.com>