Remove gRPC

Makefile

client/client.go

cmd/cashier/main.go

proto/signer.pb.go

proto/signer.proto

server/rpc.go

server/server.go

server/signer/signer.go

vendor/github.com/golang/protobuf/proto/encode.go

vendor/github.com/golang/protobuf/proto/lib.go

vendor/github.com/golang/protobuf/proto/properties.go

vendor/github.com/golang/protobuf/proto/table_marshal.go

vendor/github.com/golang/protobuf/proto/table_unmarshal.go

vendor/github.com/golang/protobuf/proto/text.go

vendor/github.com/golang/protobuf/proto/text_parser.go

vendor/go.opencensus.io/plugin/ocgrpc/client.go

vendor/go.opencensus.io/plugin/ocgrpc/client_metrics.go

...or/go.opencensus.io/plugin/ocgrpc/client_stats_handler.go

vendor/go.opencensus.io/plugin/ocgrpc/doc.go

vendor/go.opencensus.io/plugin/ocgrpc/server.go