Remove a use of 'warn'.

'warn' isn't defined when tools are turned off.

And this warning wasn't that important.

BUG=aomedia:2310

Change-Id: If402549ea9a290088294c5d0199024ab042f4e24
diff --git a/av1/av1_cx_iface.c b/av1/av1_cx_iface.c
index 199ef0a..285e6a5 100644
--- a/av1/av1_cx_iface.c
+++ b/av1/av1_cx_iface.c
@@ -25,7 +25,6 @@
 #include "av1/encoder/bitstream.h"
 #include "av1/encoder/encoder.h"
 #include "av1/encoder/firstpass.h"
-#include "common/tools_common.h"
 
 #define MAG_SIZE (4)
 #define MAX_NUM_ENHANCEMENT_LAYERS 3
@@ -727,9 +726,6 @@
   oxcf->max_reference_frames = extra_cfg->max_reference_frames;
   if (oxcf->max_reference_frames > 3 && oxcf->max_reference_frames < 7) {
     // TODO(urvang): Enable all possible values, after they work properly.
-    warn(
-        "max_reference_frames values between 3 and 7 are not supported yet. "
-        "Using value 3 instead.");
     oxcf->max_reference_frames = 3;
   }
   oxcf->enable_masked_comp = extra_cfg->enable_masked_comp;