Dockerfile should set the syntax directive to v1 (#125632)

Fixes #125526 [#1811](https://github.com/pytorch/builder/issues/1811)

Adopt syntax=docker/dockerfile:1 whcih has been stable since 2018, while still best practice to declare in 2024.
- Syntax features dependent upon the [syntax directive version are documented here](https://hub.docker.com/r/docker/dockerfile).
- While you can set a fixed minor version, [Docker officially advises to only pin the major version]

```
(https://docs.docker.com/build/dockerfile/frontend/#stable-channel):
We recommend using docker/dockerfile:1, which always points to the latest stable release of the version 1 syntax, and receives both "minor" and "patch" updates for the version 1 release cycle.
BuildKit automatically checks for updates of the syntax when performing a build, making sure you are using the most current version.
```

**Support for building with Docker prior to v23 (released on Feb 2023)**
NOTE: 18.06 may not be the accurate minimum version for using docker/dockerfile:1, according to the [DockerHub tag history](https://hub.docker.com/layers/docker/dockerfile/1.0/images/sha256-92f5351b2fca8f7e2f452aa9aec1c34213cdd2702ca92414eee6466fab21814a?context=explore) 1.0 of the syntax seems to be from Dec 2018, which is probably why docker/dockerfile:experimental was paired with it in this file.

Personally, I'd favor only supporting builds with Docker v23. This is only relevant for someone building this Dockerfile locally, the user could still extend the already built and published image from a registry on older versions of Docker without any concern for this directive which only applies to building this Dockerfile, not images that extend it.

However if you're reluctant, you may want to refer others to [this Docker docs page](https://docs.docker.com/build/buildkit/#getting-started) where they should only need the ENV DOCKER_BUILDKIT=1, presumably the requirement for experimental was dropped with syntax=docker/dockerfile:1 with releases of Docker since Dec 2018. Affected users can often quite easily install a newer version of Docker on their OS, as per Dockers official guidance (usually via including an additional repo to the package manager).

**Reference links**
Since one of these was already included in the inline note (now a broken link), I've included relevant links mentioned above. You could alternatively rely on git blame with a commit message referencing the links or this PR for more information.

Feel free to remove any of the reference links, they're mostly only relevant to maintainers to be aware of (which this PR itself has detailed adequately above).

Pull Request resolved: https://github.com/pytorch/pytorch/pull/125632
Approved by: https://github.com/malfet

docker.Makefile

@@ -57,8 +57,7 @@ PUSH_FLAG                 = --push
 endif
 endif
 
-DOCKER_BUILD              = DOCKER_BUILDKIT=1 \
-							docker $(BUILD) \
+DOCKER_BUILD              = docker $(BUILD) \
 								--progress=$(BUILD_PROGRESS) \
 								$(EXTRA_DOCKER_BUILD_FLAGS) \
 								$(PLATFORMS_FLAG) \