metropolis/pkg/tpm: replace external errors package with stdlib

Change-Id: Icacaf8b4a189d7b3cb9b516007ce4796da010573
Reviewed-on: https://review.monogon.dev/c/monogon/+/3039
Tested-by: Jenkins CI
Reviewed-by: Serge Bazanski <serge@monogon.tech>
diff --git a/metropolis/pkg/tpm/tpm.go b/metropolis/pkg/tpm/tpm.go
index 876d61f..f005399 100644
--- a/metropolis/pkg/tpm/tpm.go
+++ b/metropolis/pkg/tpm/tpm.go
@@ -22,6 +22,7 @@
 	"crypto/rand"
 	"crypto/rsa"
 	"crypto/x509"
+	"errors"
 	"fmt"
 	"io"
 	"os"
@@ -34,7 +35,6 @@
 	tpm2tools "github.com/google/go-tpm-tools/client"
 	"github.com/google/go-tpm/tpm2"
 	"github.com/google/go-tpm/tpmutil"
-	"github.com/pkg/errors"
 	"golang.org/x/crypto/nacl/secretbox"
 	"golang.org/x/sys/unix"
 	"google.golang.org/protobuf/proto"