(PUP-9997) Remove dead code

The Puppet::Util::Reference.pdf method has been broken since 2012 due to
commit f0c9995, because it was calling
Puppet::Util.replace_file with 1 argumentm, but it takes 2, resulting
in:

    $ puppet doc --mode pdf --reference type
    creating pdf
    Error: Could not run: wrong number of arguments (given 1, expected 2)

So delete the code and remove `pdf` as a valid reference doc mode.

Author: joshcooper

lib/puppet/application/doc.rb

@@ -173,11 +173,7 @@ def other
 
     text += Puppet::Util::Reference.footer unless with_contents # We've only got one reference
 
-    if options[:mode] == :pdf
-      Puppet::Util::Reference.pdf(text)
-    else
-      puts text
-    end
+    puts text
 
     exit exit_code
   end

lib/puppet/util/reference.rb

@@ -13,7 +13,7 @@ class Puppet::Util::Reference
   instance_load(:reference, 'puppet/reference')
 
   def self.modes
-    %w[pdf text]
+    %w[text]
   end
 
   def self.newreference(name, options = {}, &block)
@@ -32,35 +32,6 @@ def self.page(*sections)
     end
   end
 
-  def self.pdf(text)
-    puts _("creating pdf")
-    rst2latex = which('rst2latex') || which('rst2latex.py') ||
-                raise(_("Could not find rst2latex"))
-
-    cmd = %(#{rst2latex} /tmp/puppetdoc.txt > /tmp/puppetdoc.tex)
-    Puppet::Util.replace_file("/tmp/puppetdoc.txt") { |f| f.puts text }
-    # There used to be an attempt to use secure_open / replace_file to secure
-    # the target, too, but that did nothing: the race was still here.  We can
-    # get exactly the same benefit from running this effort:
-    begin
-      Puppet::FileSystem.unlink('/tmp/puppetdoc.tex')
-    rescue
-      nil
-    end
-    output = %x(#{cmd})
-    unless $CHILD_STATUS == 0
-      $stderr.puts _("rst2latex failed")
-      $stderr.puts output
-      exit(1)
-    end
-    $stderr.puts output
-
-    # Now convert to pdf
-    Dir.chdir("/tmp") do
-      %x(texi2pdf puppetdoc.tex >/dev/null 2>/dev/null)
-    end
-  end
-
   def self.references(environment)
     instance_loader(:reference).loadall(environment)
     loaded_instances(:reference).sort_by(&:to_s)