The Zero op right after newobject has been removed. But this rule
does not cover Store of constant zero (for SSA-able types). Add
rules to cover Store op as well.

Updates #19027.

Change-Id: I5d2b62eeca0aa9ce8dc7205b264b779de01c660b
Reviewed-on: https://go-review.googlesource.com/36836
Run-TryBot: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>