driver/docker-container: remove uses of dockerclient.IsErrNotFound

[thaJeztah]

It's a wrapper around errdefs.IsNotFound, which is already used, so we can skip the wrapper.

buildx/vendor/github.com/docker/docker/client/errors.go

Lines 42 to 46 in 934841f

	// IsErrNotFound returns true if the error is a NotFound error, which is returned
	// by the API when some object is not found. It is an alias for [errdefs.IsNotFound].
	func IsErrNotFound(err error) bool {
	return errdefs.IsNotFound(err)
	}