This reverts commit 05050cdb23,
not all places that use e.g. OStringToOUString to convert potential UTF-8
are guaranteed to fulfil the prerequisites necessary to use fromUtf8 (and
some places like e.g. in codemaker are happy with the best-effort effect
of OStringToOUString's OSTRING_TO_OUSTRING_CVTFLAGS).
l10ntools (l10n = localization) contains a number of tools that extract translatable content from source code and merge translations back to source code during the build.