Removes the base_product check from is_suma functions

[apozsuse]

Suma 5 payg images are not identified properly by the is_suma_server function, as the function was checking the baseproduct to be the Suma server one.

For Suma 5 images the baseproduct is the one for Micro, but the /etc/products.d contains also the suma-server one.

lrwxrwxrwx. 1 root root   14 sep 17 08:14 baseproduct -> SLE-Micro.prod
-rw-r--r--. 1 root root 1558 feb 28  2024 SLE-Micro.prod
-rw-r--r--. 1 root root 1939 ago 19 09:24 SUSE-Manager-Server.prod

This PR removes the baseproduct check in those functions and just leaves the file check for Suma server.

[aosthof]

Except for the one comment this LGTM.