all: clean up minor issues found by staticcheck

Use bytes.Equal instead of comparing bytes.Compare results to zero,
avoid Yoda conditions, drop a redundant zero slice capacity, use
strings.ReplaceAll, build acme error strings with a strings.Builder,
and lowercase an error string in ocsp. No behavior changes.

Change-Id: I5d2b3fa5c241adc75e61be0f2d2d7af1eb9e8d66
Reviewed-on: https://go-review.googlesource.com/c/crypto/+/803200
Reviewed-by: Roland Shoemaker <roland@golang.org>
Auto-Submit: Roland Shoemaker <roland@golang.org>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Carlos Amedee <carlos@golang.org>

ocsp/ocsp.go

@@ -322,7 +322,7 @@ type Request struct {
 func (req *Request) Marshal() ([]byte, error) {
 	hashAlg := getOIDFromHashAlgorithm(req.HashAlgorithm)
 	if hashAlg == nil {
-		return nil, errors.New("Unknown hash algorithm")
+		return nil, errors.New("unknown hash algorithm")
 	}
 	return asn1.Marshal(ocspRequest{
 		TBSRequest: tbsRequest{

ocsp/ocsp_test.go

@@ -195,7 +195,7 @@ func TestOCSPRequest(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	if bytes.Compare(expectedBytes, marshaledRequest) != 0 {
+	if !bytes.Equal(expectedBytes, marshaledRequest) {
 		t.Errorf(
 			"Marshaled request doesn't match expected: wanted %x, got %x",
 			expectedBytes,