After the refactoring to optionally use libjpeg-turbo, some
of the functions that mjpeg-encoder used to provide are now no
longer used. This commit removes them.
This API is meant to allow us to move the pixel format conversion
into MjpegEncoder. This will allow us to be able to use the
additional pixel formats from libjpeg-turbo when available.
When encoding a frame, red_worker passes an allocated buffer to
libjpeg where it should encode the frame. When it fails, a new
bigger buffer is allocated and the encoding is restarted from
scratch. However, it's possible to use libjpeg to realloc this
buffer if it gets too small during the encoding process. Make use
of this feature, especially since it will make it easier to encore
one line at a time instead of a full frame in subsequent commits.
