cmd/compile: disable name preservation on copies in expand_calls

Apparently CL 309330 caused the compiler OOMing on some large
input (giant generated switch statement). I don't quite understand
it for now. Disable it for now.

Change-Id: I19c84f3f5e158897bff0b32d6217fcff3c66874d
Reviewed-on: https://go-review.googlesource.com/c/go/+/311829


Trust: Cherry Zhang <cherryyz@google.com>
Run-TryBot: Cherry Zhang <cherryyz@google.com>
Reviewed-by: Than McIntosh <thanm@google.com>
TryBot-Result: Go Bot <gobot@golang.org>