Prep for subsequent CLs to remove old escape analysis pass.

This CL removes -newescape=true from tests that use it, and deletes
tests that use -newescape=false. (For history, see CL 170447.)

Notably, this removes escape_because.go without any replacement, but
this is being tracked by #31489.

Change-Id: I6f6058d58fff2c5d210cb1d2713200cc9f501ca7
Reviewed-on: https://go-review.googlesource.com/c/go/+/187617
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Robert Griesemer <gri@golang.org>