Remove unnecessary calls to ithread_exit

The ithread_exit wrapper function behaves inconsistently across
platforms; on windows, the argument is a thread handle, denoting
the thread that will be exited. On pthreads, ithread_exit only
terminates the current thread, not any other thread.

These both calls are at the end of each thread function (and the one
with a non-null parameter refers to the handle of the thread itself),
so the thread will exit immediately anyway.

Change-Id: I21e43c56874729452bd80b28ff351e3c5d3f087e

decoder/ih264d_thread_parse_decode.c

@@ -633,8 +633,6 @@ void ih264d_decode_picture_thread(dec_struct_t *ps_dec )
                               ps_dec->u4_fmt_conv_num_rows);
         ps_dec->u4_fmt_conv_cur_row += ps_dec->u4_fmt_conv_num_rows;
     }
-
-    ithread_exit(0);
 }
 
 void ih264d_signal_decode_thread(dec_struct_t *ps_dec)