ans: Move buf_ans_flush to the .c file

It is called relatively rarely and doesn't need to be inlined.

Change-Id: I4ee7f95548f008f2ee29da807aaca54b9a25aecd
diff --git a/test/ans_test.cc b/test/ans_test.cc
index e3ea14a..4c63352 100644
--- a/test/ans_test.cc
+++ b/test/ans_test.cc
@@ -56,7 +56,7 @@
   for (PvVec::const_iterator it = pv_vec.begin(); it != pv_vec.end(); ++it) {
     buf_uabs_write(&a, it->second, 256 - it->first);
   }
-  buf_ans_flush(&a);
+  aom_buf_ans_flush(&a);
   std::clock_t enc_time = std::clock() - start;
   int offset = buf_ans_write_end(&a);
   aom_buf_ans_free(&a);
@@ -125,7 +125,7 @@
        it != sym_vec.end(); ++it) {
     buf_rans_write(&a, &tab[*it]);
   }
-  buf_ans_flush(&a);
+  aom_buf_ans_flush(&a);
   std::clock_t enc_time = std::clock() - start;
   int offset = buf_ans_write_end(&a);
   aom_buf_ans_free(&a);