Move daala_fdst4() / daala_idst4() into daala_tx.c.

This commit has no impact on metrics.

Change-Id: I85007ef966b9aab4545499016ed68ab5c96a417a
diff --git a/av1/common/idct.c b/av1/common/idct.c
index a9bfb9a..b4e3f04 100644
--- a/av1/common/idct.c
+++ b/av1/common/idct.c
@@ -331,23 +331,23 @@
 #endif
   static const transform_2d IHT_4[] = {
 #if CONFIG_DAALA_DCT4
-    { daala_idct4, daala_idct4 },    // DCT_DCT  = 0
-    { aom_iadst4_c, daala_idct4 },   // ADST_DCT = 1
-    { daala_idct4, aom_iadst4_c },   // DCT_ADST = 2
-    { aom_iadst4_c, aom_iadst4_c },  // ADST_ADST = 3
+    { daala_idct4, daala_idct4 },  // DCT_DCT  = 0
+    { daala_idst4, daala_idct4 },  // ADST_DCT = 1
+    { daala_idct4, daala_idst4 },  // DCT_ADST = 2
+    { daala_idst4, daala_idst4 },  // ADST_ADST = 3
 #if CONFIG_EXT_TX
-    { aom_iadst4_c, daala_idct4 },   // FLIPADST_DCT
-    { daala_idct4, aom_iadst4_c },   // DCT_FLIPADST
-    { aom_iadst4_c, aom_iadst4_c },  // FLIPADST_FLIPADST
-    { aom_iadst4_c, aom_iadst4_c },  // ADST_FLIPADST
-    { aom_iadst4_c, aom_iadst4_c },  // FLIPADST_ADST
-    { iidtx4_c, iidtx4_c },          // IDTX
-    { daala_idct4, iidtx4_c },       // V_DCT
-    { iidtx4_c, daala_idct4 },       // H_DCT
-    { aom_iadst4_c, iidtx4_c },      // V_ADST
-    { iidtx4_c, aom_iadst4_c },      // H_ADST
-    { aom_iadst4_c, iidtx4_c },      // V_FLIPADST
-    { iidtx4_c, aom_iadst4_c },      // H_FLIPADST
+    { daala_idst4, daala_idct4 },  // FLIPADST_DCT
+    { daala_idct4, daala_idst4 },  // DCT_FLIPADST
+    { daala_idst4, daala_idst4 },  // FLIPADST_FLIPADST
+    { daala_idst4, daala_idst4 },  // ADST_FLIPADST
+    { daala_idst4, daala_idst4 },  // FLIPADST_ADST
+    { iidtx4_c, iidtx4_c },        // IDTX
+    { daala_idct4, iidtx4_c },     // V_DCT
+    { iidtx4_c, daala_idct4 },     // H_DCT
+    { daala_idst4, iidtx4_c },     // V_ADST
+    { iidtx4_c, daala_idst4 },     // H_ADST
+    { daala_idst4, iidtx4_c },     // V_FLIPADST
+    { iidtx4_c, daala_idst4 },     // H_FLIPADST
 #endif
 #else
     { aom_idct4_c, aom_idct4_c },    // DCT_DCT  = 0