go.tools/dashboard/app: remove redundant transaction
go.tools/dashboard/app: remove redundant transaction

The code is already called from inside a transaction.

TBR=dvyukov
R=dvyukov
CC=golang-codereviews
https://golang.org/cl/161580045

evandbrown/build,evandbrown/build,proppy/build,proppy/build,golang/build,golang/build,proppy/build,proppy/build,golang/build,evandbrown/build,golang/build