Remove texture-based video processing in NvDecoder

- Removes TextureObject class and related texture management code
- Replaces texture-based convert_frame with direct VideoColorSpaceConversion
- Removes textures_ member and get_textures method
- Unifies the video reader with the experimental one by removing texture usage which don't
  provide much gain in this use case

Signed-off-by: Janusz Lisiecki <[email protected]>

Author: JanuszL