Camera: Remove an unused method in HidlCamera3Device.h

`void notify(const hardware::camera::device::V3_2::NotifyMsg& msg);`
has remained in Camera3Device.h, but it's not used.

Bug: 269394418

Change-Id: Id0162ad3392d46a6be53977acf73544a97df3e0f
Signed-off-by: Euisang Lim <eui-sang.lim@samsung.com>