c++ api - remove get_removed_devices method from event_information class

[matkatz]

Jira issue:
DS5DSO-10869 - OnDeviceChange provide a removed list which cause crash on enumeration

The current API allows the user to iterate the removed devices list as following:

    ctx.set_devices_changed_callback([&](rs2::event_information& info)
    {
        for (auto& d : info.get_removed_devices()) { }
    });

This code will always throw exception since iterating the list tries to create the devices in the list.
And since the device is not available, exception is thrown.

The correct way to check if a device was removed is:

    ctx.set_devices_changed_callback([&](rs2::event_information& info)
    {
        if (info.was_removed(my_device))
            handle_device_removale();
    });

[dorodnic]

Please add more information on the reason for this change