controller: remove controller grpc service

Remove the controller grpc service along with associated code related to
sessions or remote controllers.

Data types that are still used with complicated dependency chains have
been kept in the same package for a future refactor.

Signed-off-by: Jonathan A. Sternberg <jonathan.sternberg@docker.com>

controller/pb/invoke.go

@@ -0,0 +1,40 @@
+package pb
+
+import (
+	"fmt"
+	"strings"
+)
+
+type CallFunc struct {
+	Name         string
+	Format       string
+	IgnoreStatus bool
+}
+
+func (x *CallFunc) String() string {
+	var elems []string
+	if x.Name != "" {
+		elems = append(elems, fmt.Sprintf("Name:%q", x.Name))
+	}
+	if x.Format != "" {
+		elems = append(elems, fmt.Sprintf("Format:%q", x.Format))
+	}
+	if x.IgnoreStatus {
+		elems = append(elems, fmt.Sprintf("IgnoreStatus:%v", x.IgnoreStatus))
+	}
+	return strings.Join(elems, " ")
+}
+
+type InvokeConfig struct {
+	Entrypoint []string
+	Cmd        []string
+	NoCmd      bool
+	Env        []string
+	User       string
+	NoUser     bool
+	Cwd        string
+	NoCwd      bool
+	Tty        bool
+	Rollback   bool
+	Initial    bool
+}