media: staging: media: atomisp: Remove unused function

The function ia_css_mipi_frame_specify() is not called from anywhere and
the comment above its declaration states that it should be removed when
there are no more users. So remove it.

Link: https://lore.kernel.org/linux-media/20201017142810.26967-1-alex.dewar90@gmail.com


Signed-off-by: Alex Dewar <alex.dewar90@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>