math/big: simplify benchmarking code some more
math/big: simplify benchmarking code some more

Follow-up cleanup to https://golang.org/cl/23424/ .

Change-Id: Ifb05c1ff5327df6bc5f4cbc554e18363293f7960
Reviewed-on: https://go-review.googlesource.com/23446
Reviewed-by: Marcel van Lohuizen <a22d082192f3ccf984644a4f482781f4c2d65180@golang.org>

ImJasonH/go,akutz/go,CAFxX/go,goodlang/good,theif519/go,josharian/go,theif519/go,akutz/go,suncycheng/go,momchil-velikov/go,codestation/go,nawawi/go,josharian/go,derekmarcotte/go,suncycheng/go,suncycheng/go,Cofyc/go,cloudflare/go,derekmarcotte/go,theif519/go,akutz/go,goodlang/good,ImJasonH/go,codestation/go,linux-on-ibm-z/go,momchil-velikov/go,derekmarcotte/go,akutz/go,CAFxX/go,suncycheng/go,golang/go,theif519/go,linux-on-ibm-z/go,Cofyc/go,theif519/go,linux-on-ibm-z/go,Cofyc/go,Cofyc/go,linux-on-ibm-z/go,vsekhar/elastic-go,momchil-velikov/go,vsekhar/elastic-go,vsekhar/elastic-go,linux-on-ibm-z/go,golang/go,Cofyc/go,Cofyc/go,suncycheng/go,CAFxX/go,polyverse-security/go,ImJasonH/go,derekmarcotte/go,momchil-velikov/go,4ad/go,goodlang/good,akutz/go,vsekhar/elastic-go,ImJasonH/go,josharian/go,goodlang/good,vsekhar/elastic-go,4ad/go,CAFxX/go,cloudflare/go,theif519/go,vsekhar/elastic-go,goodlang/good,polyverse-security/go,golang/go,nawawi/go,polyverse-security/go,Cofyc/go,cloudflare/go,nawawi/go,vsekhar/elastic-go,suncycheng/go,4ad/go,cloudflare/go,codestation/go,derekmarcotte/go,CAFxX/go,ImJasonH/go,polyverse-security/go,josharian/go,momchil-velikov/go,golang/go,goodlang/good,codestation/go,nawawi/go,ImJasonH/go,linux-on-ibm-z/go,cloudflare/go,golang/go,4ad/go,nawawi/go,suncycheng/go,CAFxX/go,josharian/go,nawawi/go,4ad/go,cloudflare/go,4ad/go,vsekhar/elastic-go,linux-on-ibm-z/go,goodlang/good,golang/go,polyverse-security/go,codestation/go,josharian/go,akutz/go,momchil-velikov/go,ImJasonH/go,codestation/go,momchil-velikov/go,derekmarcotte/go,christopher-henderson/Go,josharian/go,ImJasonH/go,suncycheng/go,codestation/go,goodlang/good,linux-on-ibm-z/go,CAFxX/go,nawawi/go,golang/go,nawawi/go,polyverse-security/go,theif519/go,derekmarcotte/go,akutz/go,theif519/go,derekmarcotte/go,codestation/go,CAFxX/go,4ad/go,akutz/go,polyverse-security/go,cloudflare/go,momchil-velikov/go,josharian/go,golang/go,cloudflare/go,4ad/go,polyverse-security/go,Cofyc/go