Merge CONFIGURE_SEGMENTATION experiment.
Removal of CONFIGURE_SEGMENTATION ifdefs. Removal of legacy support code fo the old coding mechanism. Use local reference "xd" for MACROBLOCKD structure in encode_frame_to_data_rate() Moved call to choose_segmap_coding_method() out of encode loop as the cost of segmentation is not properly accounted in the loop anyway. If this is desirable in the future it can be moved back. The use of this function to do all the analysis and set the probabilities also removes the need to track segment useage in threading code. Change-Id: I85bc8fd63440e7176c73d26cb742698f9b70cade