Remove multiple coefficient buffers from PICK_MODE_CONTEXT

The swap_block_ptr functionality was removed by
0d6980d7a1caa592058f8d5d618b012c160772f7 in nextgenv2.

This patch removes all the code removed in nextgenv2 and deletes
some now unnecessary left over struct members as well.

Change-Id: I1e22514c6fe5af556710254278f2f8a5805db999
7 files changed