Remove unused span (#1599)

Author: davidfowl

src/Microsoft.AspNetCore.Server.Kestrel.Core/Internal/Http/KestrelHttpParser.cs

@@ -181,8 +181,6 @@ private unsafe void ParseRequestLine<T>(T handler, byte* data, int length) where
                 RejectRequestLine(data, length);
             }
 
-            var line = new Span<byte>(data, length);
-
             handler.OnStartLine(method, httpVersion, targetBuffer, pathBuffer, query, customMethod, pathEncoded);
         }