* src/dn.cpp: Add missing includes. Use std::literals namespace.
(removeLeadingSpaces, removeTrailingSpaces): Use npos to check result of
find_first_not_of/find_last_not_of.
(parseHexString): Constify size variable. Replace const char * literal
with string_view literal. Use size instead of view.size() in end
condition of for-loop.
(attributeNameForOID): Replace string_view constructed from const char *
literals with string_view literals.
(parse_dn_part): Replace const char * literal with string_view literal.
Remove validation of hexstring which is already done by parseHexString.
Use string_view::remove_prefix instead of string_view::substr.
(parse_dn): Constify parsed variable.