media: mantis: remove orphan mantis_core.c

There is no Makefile rule to have drivers/media/pci/mantis/mantis_core.o
in build since the code overhaul with commit b3b96144
("V4L/DVB (13795): [Mantis/Hopper] Code overhaul, add Hopper devices into the PCI ID list").

It looks like drivers/media/pci/mantis/mantis_core.c is a leftover.

Remove the orphan code.

Link: https://lore.kernel.org/linux-media/20200922132221.2051769-1-fazilyildiran@gmail.com


Fixes: b3b96144 ("V4L/DVB (13795): [Mantis/Hopper] Code overhaul, add Hopper devices into the PCI ID list").
Signed-off-by: Necip Fazil Yildiran <fazilyildiran@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>