test: don't rely on order of unrelated imports in bug191

test: don't rely on order of unrelated imports in bug191

There is no necessary relationship between the imports of the
packages a and b, and gccgo happens to import them in a
different order, leading to different output.  This ordering
is not the purpose of the test in any case.

R=golang-dev, rsc
CC=golang-dev
https://golang.org/cl/40400043