Remove RDoc::RDoc#exclude

The property is copied from @options and not used. It's inappropriately
complicated for the processing the option.

lib/rdoc/rdoc.rb

@@ -35,11 +35,6 @@ class RDoc::RDoc
 
   GENERATORS = {}
 
-  ##
-  # File pattern to exclude
-
-  attr_accessor :exclude
-
   ##
   # Generator instance used for creating output
 
@@ -93,7 +88,6 @@ def self.current= rdoc
 
   def initialize
     @current       = nil
-    @exclude       = nil
     @generator     = nil
     @last_modified = {}
     @old_siginfo   = nil
@@ -116,7 +110,7 @@ def error(msg)
   def gather_files files
     files = ["."] if files.empty?
 
-    file_list = normalized_file_list files, true, @exclude
+    file_list = normalized_file_list files, true, @options.exclude
 
     file_list = file_list.uniq
 
@@ -472,8 +466,6 @@ def document options
       exit
     end
 
-    @exclude = @options.exclude
-
     unless @options.coverage_report then
       @last_modified = setup_output_dir @options.op_dir, @options.force_update
     end