Fix warning.

Signed-off-by: Stefan Westerfeld <stefan@space.twc.de>

src/audiowmark.cc

@@ -850,7 +850,6 @@ public:
           }
         if ((f % Params::sync_frames_per_bit) == (Params::sync_frames_per_bit - 1))
           {
-            const int data_bit = (umag < dmag) ? 0 : 1;
             const int expect_data_bit = (f / Params::sync_frames_per_bit) & 1; /* expect 010101 */
 
             const double q = expect_data_bit ? (1 - umag / dmag) : (umag / dmag - 1);