The theory is that

- the operator is suboptimal, because it always uses utf-8 as the encoding,
  which might possibly lead to some encoding problem somewhere

but

- the SAL_LOG macros need it anyway, or they are otherwise cumbersome
  with OUString
- as people learn to use the macros more, rtl/oustringostreaminserter.hxx
  will be included in more and more places, eventually possibly triggering
  the above problem anyway
- people probably should not just blindly do ostream << oustring if they
  have special encoding requirements

So let's try to simply always have the operator available and see how
it works out.