[account.cpp] remove unused static var

libgnucash/engine/Account.cpp

@@ -4798,13 +4798,10 @@ dxaccAccountSetPriceSrc(Account *acc, const char *src)
 const char*
 dxaccAccountGetPriceSrc(const Account *acc)
 {
-    static char *source = nullptr;
     if (!acc) return nullptr;
 
     if (!xaccAccountIsPriced(acc)) return nullptr;
 
-    g_free (source);
-
     return get_kvp_string_path (acc, {"old-price-source"});
 }