cmd/go: fix bug in test of go get ./path needing to download path
cmd/go: fix bug in test of go get ./path needing to download path

rsc.io/toolstash is gone; use rsc.io/pprof_mac_fix.

This fixes a bug in the test. It turns out the code being tested here
is also broken, so the test still doesn't pass after this CL (filed #19769).

Change-Id: Ieb725c321d7fab600708e133ae28f531e55521ad
Reviewed-on: https://go-review.googlesource.com/38743
Reviewed-by: Alan Donovan <7069e9552f9d110b0a0f326b96f22f63fb99dfc1@google.com>

polyverse-security/go,codestation/go,vsekhar/elastic-go,Cofyc/go,josharian/go,codestation/go,polyverse-security/go,nawawi/go,vsekhar/elastic-go,CAFxX/go,cloudflare/go,nawawi/go,codestation/go,cloudflare/go,codestation/go,CAFxX/go,akutz/go,derekmarcotte/go,linux-on-ibm-z/go,polyverse-security/go,polyverse-security/go,derekmarcotte/go,golang/go,golang/go,josharian/go,linux-on-ibm-z/go,nawawi/go,akutz/go,codestation/go,CAFxX/go,josharian/go,CAFxX/go,CAFxX/go,josharian/go,akutz/go,golang/go,cloudflare/go,nawawi/go,polyverse-security/go,ImJasonH/go,ImJasonH/go,CAFxX/go,christopher-henderson/Go,linux-on-ibm-z/go,akutz/go,nawawi/go,ImJasonH/go,derekmarcotte/go,derekmarcotte/go,josharian/go,CAFxX/go,golang/go,cloudflare/go,cloudflare/go,CAFxX/go,derekmarcotte/go,vsekhar/elastic-go,vsekhar/elastic-go,akutz/go,cloudflare/go,vsekhar/elastic-go,polyverse-security/go,akutz/go,josharian/go,ImJasonH/go,Cofyc/go,derekmarcotte/go,codestation/go,golang/go,codestation/go,derekmarcotte/go,akutz/go,nawawi/go,linux-on-ibm-z/go,codestation/go,cloudflare/go,golang/go,ImJasonH/go,Cofyc/go,golang/go,akutz/go,ImJasonH/go,linux-on-ibm-z/go,linux-on-ibm-z/go,polyverse-security/go,Cofyc/go,cloudflare/go,linux-on-ibm-z/go,Cofyc/go,nawawi/go,derekmarcotte/go,ImJasonH/go,vsekhar/elastic-go,ImJasonH/go,vsekhar/elastic-go,Cofyc/go,golang/go,Cofyc/go,vsekhar/elastic-go,polyverse-security/go,linux-on-ibm-z/go,josharian/go,josharian/go,nawawi/go,Cofyc/go