crypto/dsa: also use fromHex in TestSignAndVerify.
crypto/dsa: also use fromHex in TestSignAndVerify.

This change contains a very minor tidy-up to a test.

Change-Id: I3a8c0168bcdcbf90cacbbac2566c8423c92129f8
Reviewed-on: https://go-review.googlesource.com/33726
Reviewed-by: Adam Langley <db68fba232b2c49ed3e9d3081df349dde7b61dfd@golang.org>
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Adam Langley <db68fba232b2c49ed3e9d3081df349dde7b61dfd@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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