rpi4: boot: remove deprecated camera dtoverlay

rpi4: boot: remove deprecated camera dtoverlay

The config.txt command 'camera_auto_detect=1' will select
a connected camera sensor dt overlay. and 'dtoverlay=camera'
is not used. Remove the deprecated camera dt overlay setting.

This will removes below firmware warning during booting:
   Failed to load overlay 'camera'
   brfs: File read: /mfs/sd/overlays/camera.dtbo

Change-Id: I5521343efb46b16fb73caee48e415214e64d33c0
Ref: https://www.raspberrypi.com/documentation/computers/camera_software.html
Signed-off-by: Seung-Woo Kim <sw0312.kim@samsung.com>