runtime: rename print1.go -> print.go

It seems that it was called print1.go mistakenly: print.go was deleted
in the same commit:
https://go.googlesource.com/go/+/597b266eafe7d63e9be8da1c1b4813bd2998a11c

Updates #12952

Change-Id: I371e59d6cebc8824857df3f3ee89101147dfffc0
Reviewed-on: https://go-review.googlesource.com/15950
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>

diff --git a/src/runtime/print1.go b/src/runtime/print.go
similarity index 100%
rename from src/runtime/print1.go
rename to src/runtime/print.go