cmd/goyacc: remove ineffective break statement

Found with honnef.co/go/tools/cmd/staticcheck.

Change-Id: I7f765ef1710d151ebda5716c99587acd3a90db1f
Reviewed-on: https://go-review.googlesource.com/38173
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
1 file changed