...now that all of its uses have been replaced with C++17 <string_view>.

The LO-specific o3tl::basic_string_view ctors with OString and OUString params
have meanwhile been replaced with OString and OUString conversion functions (in
dac7be50 "o3tl::string_view -> std::string_view
(in configmgr)"), the ctor with OUStringLiteral turned out to be no longer(?)
needed anyway, and the LO-specific o3tl::toOUString has meanwhile been replaced
with an OUString ctor with std::u16string_view param (in
6856da30 "o3tl::string_view -> std::string_view
(in embedserv)").

Change-Id: Ie5215b07e2387560fb7e94de8b5a963241539c64
Reviewed-on: https://gerrit.libreoffice.org/66144
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>