Remove a dead variable from ldmd. (It used to be used to pass an extra -help to ldc when no files were specified, but we handle that in ldc itself now)

module union1;

union U
{
    float f;
    int i;
}

void main()
{
    float f = 2;
    U u = U(f);
    assert(u.i == *cast(int*)&f);
}