Remove the cbs creation for n900 plugin, this lead to crashes on n9 ofon...

...o init.

For the latest release of ofono for Nemo Mobile, the modem fails to initialize
with the isimodem driver enabled. This is due to a segmentation fault occurring
in the flush of the atoms of the modem in cbs_assembly_free function. This
resulted in a segmentation fault when using n900 driver.

[n900] Remove cbs creation.
Just commenting out without explanation looks more of a hack/unclean, possibly that's why it also never made upstream as-was in 2012.
I'm not familiar how ofono patches are proposed upstream, could you please comment more @jpoutiai ?