Ruby » Ruby master

Revert r33924.

• proc.c (rb_proc_arity): Fix Proc#arity in case of optional arguments
  [bug #5694] [rubyspec:b8b259] [rubyspec:184c8100f]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@36411 b2dd03c8-39d4-4d8f-98ff-823fe69b080e