remove infra link from index.rst

Signed-off-by: Avinash Mehta <avinash.mehta@arm.com>

index.rst

 Welcome to Arm reference solutions documentation!
 ===================================================
 
-.. toctree::
-   :maxdepth: 2
-   :caption: Infra:
-
-   docs/infra/readme
-
 .. toctree::
    :maxdepth: 2
    :caption: Total Compute: