Unnecessary rate distortion calculations 

Originally reported on Google Code with ID 479

```
opj_t1_getnmsedec_sig() method is passed  (bitpos + T1_NMSEDEC_FRACBITS)
and then uses (bitpos - T1_NMSEDEC_FRACBITS) in its computations.

No need to add, and then subtract, T1_NMSEDEC_FRACBITS.  

Likewise for opj_t1_getnmsedec_ref() method.



```

Reported by [boxerab](https://github.com/boxerab) on 2015-03-11 00:38:50
