Makefile.uk: Remove forceful setting of config

Makefile.uk: Remove forceful setting of config

Previously the python Makefile would forcefully set the Kconfig value
`STACK_SIZE_PAGE_ORDER` to 10, a minimum value for python to work.
This change removes this fairly invasive behavior in favor of an
explicit check and error message if the value is too low.

Signed-off-by: Andrei Tatar <andrei@unikraft.io>
Reviewed-by: Maria Sfiraiala <maria.sfiraiala@gmail.com>
Reviewed-by: Stefan Jumarea <stefanjumarea02@gmail.com>
Approved-by: Razvan Deaconescu <razvand@unikraft.io>
Tested-by: Unikraft CI <monkey@unikraft.io>
GitHub-Closes: #15