token-server: Add protos for new API for generating service account tokens.

server/auth/delegation_test.go

Index: server/auth/delegation_test.go
diff --git a/server/auth/delegation_test.go b/server/auth/delegation_test.go
index 967bf3725f8b2db25ba550b139270261374a4e36..b4c61aaa4d5702cc7d2f0a52e4ccf061f0f568b7 100644
--- a/server/auth/delegation_test.go
+++ b/server/auth/delegation_test.go
@@ -28,10 +28,6 @@ type tokenMinterMock struct {
 	err      error
 }
 
-func (m *tokenMinterMock) MintMachineToken(context.Context, *minter.MintMachineTokenRequest, ...grpc.CallOption) (*minter.MintMachineTokenResponse, error) {
-	panic("not implemented")
-}
-
 func (m *tokenMinterMock) MintDelegationToken(ctx context.Context, in *minter.MintDelegationTokenRequest, opts ...grpc.CallOption) (*minter.MintDelegationTokenResponse, error) {
 	m.request = *in
 	if m.err != nil {