media: atomisp: get rid of some non-existing functions for ISP2401

There are no ia_css_set_system_mode() nor
ia_css_is_system_mode_suspend_or_resume() functions at the driver.

So, get rid of the code that would try to call it.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>