clock: don't include the delay for the master clock

If the source is the master, it need to handle the delay itself by delaying the playback by the delta returned by vlc_clock_SetDelay() (for slaves, the return value will be always 0). This is already done by the audio output, that is sending silence to reach that delta.

The delay was applied 2 times, one time in the audio output and one time in the clock. Therefore, remove that extra delay.