cmd/gc: remove ignored debugging arguments in Fconv print
cmd/gc: remove ignored debugging arguments in Fconv print

LGTM=dave
R=golang-codereviews, dave
CC=golang-codereviews
https://codereview.appspot.com/123880043

tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go,tv42/old-go