Delete micro-benchmarks/nccl-tests/nccl-tests-gb200.Dockerfile (#844)

* Delete micro-benchmarks/nccl-tests/nccl-tests-gb200.Dockerfile

This file is redundant, main file will work with GB200

* Add instructions for building with platform for arm64

---------

Co-authored-by: Aman Shanbhag <55571601+amanshanbhag@users.noreply.github.com>

Author: pbelevich

micro-benchmarks/nccl-tests/README.md

@@ -68,6 +68,7 @@ If you wish to build the containar image by yourself, follow this section. Alter
           -t ${CONTAINER_IMAGE_NAME_TAG} \
           .
    ```
+   Note: If you are using an arm64 platform (like p6e-gb200.36xlarge, or any ultraserver comprised of that instance, for example), pass in `--platform=linux/arm64` into the `docker build` command above. Or, just build your image directly on an `arm64` based instance!
 
 1. Once the container image is prepared, you can check if it is present with `docker images`. You should see an output similar to this one:
    ```