go-tour: remove last slide memory
go-tour: remove last slide memory

I've had a few reports that this is confusing. Maybe it could come back
at some point in another form (eg, "Welcome back! Do you want to resume
from where you left off?").

R=golang-dev, dsymonds
CC=golang-dev
http://codereview.appspot.com/6206101

golang-tr/go-tour-tr,golang-tr/go-tour-tr