* compile.c (iseq_compile_each): remove redundant trace(line)
  instruction. for example, at the following script
  def m()
  p:xyzzy
  1
  2
  end
  compiler ignores `1' because there is no effect. However,
  `trace(line)' instruction remains in bytecode.
  This modification removes such redundant trace(line) instruction.
* test/ruby/test_iseq.rb: add a test.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39539 b2dd03c8-39d4-4d8f-98ff-823fe69b080e