Issue on explicit weighted prediction(related to #1215 )

[swlim]

In VTM, there is unnecessary condition (related to #1225).

In addWeightUni(..), two variables are set to as follows:

const int shiftNum = std::max<int>(2, (IF_INTERNAL_PREC - clipBD));
const int shift = wp0[compID].shift + shiftNum;

Therefore, the value of the variable shift is always larger than 1, it is suggested that the following code

const int  round = (shift > 0) ? (1 << (shift - 1)) : 0;

should be replaced by

const int  round = 1 << (shift - 1);