mkconstants.rb: remove empty comments

* ext/etc/mkconstants.rb: remove empty comments, defaut_proc isn't
  called by accessing nil-assigned elements, and the same content
  is useless.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46712 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
fake.rb.in: override File::ALT_SEPARATOR

* template/fake.rb.in (File::ALT_SEPARATOR): override
  ALT_SEPARATOR if different, not only a backslash.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@46713 b2dd03c8-39d4-4d8f-98ff-823fe69b080e