remove duplicate const from vpx_codec_iface_t use

the public typedef already includes a const, quiets
'same type qualifier used more than once' warnings

Change-Id: Ib118b3b116fba59d4c6ead84d85b26e5d3ed363d

test/encode_test_driver.h

diff --git a/test/encode_test_driver.h b/test/encode_test_driver.h
index dbdc33c..4dabcd5 100644
--- a/test/encode_test_driver.h
+++ b/test/encode_test_driver.h
@@ -128,7 +128,7 @@
   }
 
  protected:
-  virtual const vpx_codec_iface_t* CodecInterface() const = 0;
+  virtual vpx_codec_iface_t* CodecInterface() const = 0;
 
   const char *EncoderError() {
     const char *detail = vpx_codec_error_detail(&encoder_);