ocsp: remove a redundant conditional expression from an if statement

cert can never be nil here. The statement was incorrectly moved in
e1a4589.

Change-Id: I1fb2aa0bb26a2ad21e6f070952365233fb39a216
Reviewed-on: https://go-review.googlesource.com/48070
Reviewed-by: Adam Langley <agl@golang.org>

ocsp/ocsp.go

@@ -502,7 +502,7 @@ func ParseResponseForCert(bytes []byte, cert, issuer *x509.Certificate) (*Respon
 	} else {
 		match := false
 		for _, resp := range basicResp.TBSResponseData.Responses {
-			if cert == nil || cert.SerialNumber.Cmp(resp.CertID.SerialNumber) == 0 {
+			if cert.SerialNumber.Cmp(resp.CertID.SerialNumber) == 0 {
 				singleResp = resp
 				match = true
 				break