Remove Walter-ism that doesn't even work in release mode.

driver/main.cpp

@@ -1074,8 +1074,7 @@ int main(int argc, char **argv)
 
         if (name && name[0] == '-' && name[1] == 0)
         {   // Write to stdout; assume it succeeds
-            int n = fwrite(buf.data, 1, buf.offset, stdout);
-            assert(n == buf.offset);        // keep gcc happy about return values
+            (void)fwrite(buf.data, 1, buf.offset, stdout);
         }
         else
         {