dashboard: fix update script It needs to remove perf results rather than build results.
dashboard: fix update script
It needs to remove perf results rather than build results.

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/164000043

magiccao/tools,sshetty10/tools,golang/tools,jdhenke/tools,matryer/tools,dmitris/tools,dmitris/tools,josharian/tools,jdhenke/tools,maddyonline/tools,jdhenke/tools,nicot/tools,golang/tools,4ad/tools,argandas/tools,argandas/tools,4ad/tools,cw2018/tools,maddyonline/tools,glasser/golang-tools,sshetty10/tools,nicot/tools,argandas/tools,glasser/golang-tools,sshetty10/tools,josharian/tools,runcom/tools,argandas/tools,magiccao/tools,syreclabs/go-tools,cmars/tools,4ad/tools,syreclabs/go-tools,golang/tools,cmars/tools,springning/tools,dmitris/tools,maddyonline/tools,runcom/tools,nicot/tools,dmitris/tools,nicot/tools,sshetty10/tools,springning/tools,cw2018/tools,maddyonline/tools,cmars/tools,cw2018/tools,runcom/tools,matryer/tools,cw2018/tools,syreclabs/go-tools,springning/tools,syreclabs/go-tools,glasser/golang-tools,glasser/golang-tools,magiccao/tools,syreclabs/go-tools,runcom/tools,golang/tools,magiccao/tools,jdhenke/tools,syreclabs/go-tools,springning/tools,matryer/tools,cmars/tools,josharian/tools,josharian/tools,golang/tools,matryer/tools