Removed unused variable in a lexer benchmark.

benchmark/lexer/bench_big_xml_time.rb

@@ -1,8 +1,7 @@
 require_relative '../../lib/oga'
 require 'benchmark'
 
-xml   = File.read(File.expand_path('../../fixtures/big.xml', __FILE__))
-lexer = Oga::XML::Lexer.new(xml)
+xml = File.read(File.expand_path('../../fixtures/big.xml', __FILE__))
 
 Benchmark.bmbm(10) do |bench|
   bench.report '10MB of XML' do