Revert "boards: bsim: fix bug with single settings file for few bsim devices"

This reverts commit 4b5cd923.

global_device_nbr is used by many bsim tests.
And many of those are now off tree in preparation of the LE-Audio
work. Removing this for cleanliness now is not nice on others.
=> Revert

Signed-off-by: Alberto Escolar Piedras <alpi@oticon.com>