auth: Remove "shared" aka "global" secrets.

server/auth/authdb/db.go

Index: server/auth/authdb/db.go
diff --git a/server/auth/authdb/db.go b/server/auth/authdb/db.go
index 8da2b69909c493fc468db01497c66c6117035a3c..46f5ceb5f648a26a523a7316b616c8ae5dd638cb 100644
--- a/server/auth/authdb/db.go
+++ b/server/auth/authdb/db.go
@@ -11,7 +11,6 @@ import (
 
 	"github.com/luci/luci-go/server/auth/identity"
 	"github.com/luci/luci-go/server/auth/signing"
-	"github.com/luci/luci-go/server/secrets"
 )
 
 // DB is interface to access a database of authorization related information.
@@ -29,12 +28,6 @@ type DB interface {
 	// datastore has issues.
 	IsMember(c context.Context, id identity.Identity, groups ...string) (bool, error)
 
-	// SharedSecrets is secrets.Store with secrets in Auth DB.
-	//
-	// Such secrets are usually generated on central Auth Service and are known
-	// to all trusted services (so that they can use them to exchange data).
-	SharedSecrets(c context.Context) (secrets.Store, error)
-
 	// GetCertificates returns a bundle with certificates of a trusted signer.
 	//
 	// Returns (nil, nil) if the given signer is not trusted.