Remove PATH update from kernal-headers stage.

The PATH update was causing issues on WSL,
it actually isnt needed, as we only want to produce the headers,
they dont compile anything, so need no tools.

See - GNUTOOLS-15168

Change-Id: I9c5c1c7a329a72a52b985fdb38d310f9d38165f1
Reviewed-on: https://eu-gerrit-1.euhpc.arm.com/c/dsg-gnu/Internal/gnu-devtools-for-arm/+/716766


Reviewed-by: Vaseeharan Vinayagamoorthy <vaseeharan.vinayagamoorthy@arm.com>
Tested-by: Service account - used by users in DSG GNU team <dgboter@arm.com>
Reviewed-by: Tamar Christina <tamar.christina@arm.com>