[VecOps] Remove expensive asserts from RVec::operator[]
[VecOps] Remove expensive asserts from RVec::operator[]

As RVec is a class template, even if ROOT is compiled with -DNDEBUG
these asserts might be compiled in user code depending on whether or
not they remember to include `-DNDEBUG` in their debug flags.
I think the performance penalty is too high w.r.t. the benefit.

olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root,olifre/root