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

vp8/encoder/onyx_int.h

@@ -220,7 +220,6 @@ typedef struct
 typedef struct
 {
     MACROBLOCK  mb;
-    int segment_counts[MAX_MB_SEGMENTS];
     int totalrate;
 } MB_ROW_COMP;
 
@@ -506,9 +505,7 @@ typedef struct VP8_COMP
 #endif
 
     unsigned char *segmentation_map;
-#if CONFIG_SEGMENTATION
     unsigned char *last_segmentation_map;
-#endif
 
     // segment threashold for encode breakout
     int  segment_encode_breakout[MAX_MB_SEGMENTS];