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>

build/build.go

@@ -19,8 +19,8 @@ import (
 	"github.com/containerd/containerd/v2/core/images"
 	"github.com/distribution/reference"
 	"github.com/docker/buildx/builder"
-	controllerapi "github.com/docker/buildx/controller/pb"
 	"github.com/docker/buildx/driver"
+	"github.com/docker/buildx/util/buildflags"
 	"github.com/docker/buildx/util/confutil"
 	"github.com/docker/buildx/util/desktop"
 	"github.com/docker/buildx/util/dockerutil"
@@ -78,8 +78,8 @@ type Options struct {
 	NoCacheFilter              []string
 	Platforms                  []ocispecs.Platform
 	Pull                       bool
-	SecretSpecs                []*controllerapi.Secret
-	SSHSpecs                   []*controllerapi.SSH
+	SecretSpecs                buildflags.Secrets
+	SSHSpecs                   []*buildflags.SSH
 	ShmSize                    opts.MemBytes
 	Tags                       []string
 	Target                     string