runtime: don't skip TestCgoCallbackGC on FreeBSD
runtime: don't skip TestCgoCallbackGC on FreeBSD

Seems to be fixed according to discussion on issue 16396.

Fixes #16396.

Change-Id: Ibac7037a24280204e48cb4d3000af524f65afd36
Reviewed-on: https://go-review.googlesource.com/33903
Run-TryBot: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

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