remove unused code (#534)

go.mod

packages/client/address.go

packages/client/bundle.go

packages/client/bundlefactory.go

packages/client/seed.go

packages/model/approvers/approvers.go

packages/model/approvers/approvers_test.go

packages/model/approvers/constants.go

packages/model/bundle/bundle.go

packages/model/bundle/bundle_test.go

packages/model/bundle/constants.go

packages/model/error.go

packages/model/meta_transaction/constants.go

packages/model/meta_transaction/meta_transaction.go

packages/model/meta_transaction/meta_transaction_test.go

packages/model/transactionmetadata/const.go

packages/model/transactionmetadata/transactionmetadata.go

packages/model/value_transaction/constants.go

packages/model/value_transaction/value_transaction.go

packages/model/value_transaction/value_transaction_test.go