controller: remove remaining parts of the controller

Removes all references to the controller and moves the remaining
sections of code to other packages.

Processes has been moved to monitor where it is used and the data
structs have been removed so buildflags is used directly. The controller
build function has been moved to the commands package.

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

monitor/commands/exec.go

@@ -5,7 +5,7 @@ import (
 	"fmt"
 	"io"
 
-	controllerapi "github.com/docker/buildx/controller/pb"
+	"github.com/docker/buildx/build"
 	"github.com/docker/buildx/monitor/types"
 	"github.com/pkg/errors"
 )
@@ -13,11 +13,11 @@ import (
 type ExecCmd struct {
 	m types.Monitor
 
-	invokeConfig *controllerapi.InvokeConfig
+	invokeConfig *build.InvokeConfig
 	stdout       io.WriteCloser
 }
 
-func NewExecCmd(m types.Monitor, invokeConfig *controllerapi.InvokeConfig, stdout io.WriteCloser) types.Command {
+func NewExecCmd(m types.Monitor, invokeConfig *build.InvokeConfig, stdout io.WriteCloser) types.Command {
 	return &ExecCmd{m, invokeConfig, stdout}
 }
 
@@ -38,7 +38,7 @@ func (cm *ExecCmd) Exec(ctx context.Context, args []string) error {
 	if len(args) < 2 {
 		return errors.Errorf("command must be passed")
 	}
-	cfg := &controllerapi.InvokeConfig{
+	cfg := &build.InvokeConfig{
 		Entrypoint: []string{args[1]},
 		Cmd:        args[2:],
 		NoCmd:      false,