[-Wunused-variable] - remove unused translatable string

libgnucash/app-utils/gnc-quotes.cpp

@@ -772,8 +772,6 @@ show_gnucash_quote(const bpt::ptree& comm_pt)
     const char* rec{C_("Finance::Quote", "recommended")};
     //Translators: Means that one of the indicated elements is required
     const char* oot{C_("Finance::Quote", "one of these")};
-    //Translators: Means that the preceding element is optional
-    const char* opt{C_("Finance::Quote", "optional")};
     //Translators: Means that a required element wasn't reported. The *s are for emphasis.
     const char* miss{C_("Finance::Quote", "**missing**")};