scan.h: rm unused get_coef_context

the last reference was removed in:
0927f2acd9 Remove some dead code about transform coefficient coding

Change-Id: I381a74375c4ecc22141caa6773e42e32cb3bff66
diff --git a/av1/common/scan.h b/av1/common/scan.h
index c5cebc1..d206586 100644
--- a/av1/common/scan.h
+++ b/av1/common/scan.h
@@ -39,13 +39,6 @@
 
 void av1_deliver_eob_threshold(const AV1_COMMON *cm, MACROBLOCKD *xd);
 
-static INLINE int get_coef_context(const int16_t *neighbors,
-                                   const uint8_t *token_cache, int c) {
-  return (1 + token_cache[neighbors[MAX_NEIGHBORS * c + 0]] +
-          token_cache[neighbors[MAX_NEIGHBORS * c + 1]]) >>
-         1;
-}
-
 static INLINE const SCAN_ORDER *get_default_scan(TX_SIZE tx_size,
                                                  TX_TYPE tx_type) {
   return &av1_scan_orders[tx_size][tx_type];