Fixed unused parameters warnings

[Kojoley]

Fixes following warnings:

In file included from ../../../boost/random.hpp:63:
../../../boost/random/discrete_distribution.hpp:95:60: warning: unused parameter 'average' [-Wunused-parameter]
    static WeightType normalize(WeightType val, WeightType average)
                                                           ^
../../../boost/random/discrete_distribution.hpp:186:66: warning: unused parameter 'weights' [-Wunused-parameter]
    static WeightType try_get_sum(const std::vector<WeightType>& weights)
                                                                 ^

[Romain-Geissler-1A]

Ping.

[jeking3]

@swatanabe I made the same changes locally to resolve these warnings; however I didn't comment out the variable name, I just removed the variable name. Easy fix for a couple of warnings...

[Romain-Geissler]

Ping @swatanabe

[Kojoley]

It looks like this will never be merged.

[jeking3]

@Kojoley We're in the middle of the boost 1.67 release cycle so I wouldn't expect anything to be merged right now.

[Kojoley]

@swatanabe If the reason of not merging this is because you prefer not commenting argument names but removing them just say me and I will do it.