v4l2_codec2: Remove request-related code from V4L2 device.

This CL removes leftover code related to V4L2 requests from the V4L2
device, as it's currently not functional nor used.

Bug: 155138142
Test: arc.VideoEncodeAccel.h264_192p_i420_vm
Change-Id: I98702a74778e84f1aec00f8f216c9c4f1c16c261