Remove unused lambda capture

str is unused in the lambda; remove it from the capture

Signed-off-by: Vernon Mauery <vernon.mauery@intel.com>

include/boost/parser/parser.hpp

@@ -1629,7 +1629,7 @@ namespace boost { namespace parser {
                     initial_elements.begin(),
                     initial_elements.end(),
                     str,
-                    [&str](auto const & a, auto b) {
+                    [](auto const & a, auto b) {
                         return a.first < b;
                     });
             };