Remove code for versions older than Ruby 2.6

Author: nobu

lib/rdoc/erbio.rb

@@ -20,12 +20,8 @@ class RDoc::ERBIO < ERB
   ##
   # Defaults +eoutvar+ to 'io', otherwise is identical to ERB's initialize
 
-  def initialize str, safe_level = nil, legacy_trim_mode = nil, legacy_eoutvar = 'io', trim_mode: nil, eoutvar: 'io'
-    if RUBY_VERSION >= '2.6'
-      super(str, trim_mode: trim_mode, eoutvar: eoutvar)
-    else
-      super(str, safe_level, legacy_trim_mode, legacy_eoutvar)
-    end
+  def initialize str, trim_mode: nil, eoutvar: 'io'
+    super(str, trim_mode: trim_mode, eoutvar: eoutvar)
   end
 
   ##

lib/rdoc/generator/darkfish.rb

@@ -778,11 +778,7 @@ def template_for file, page = true, klass = ERB
       erbout = "_erbout_#{file_var}"
     end
 
-    if RUBY_VERSION >= '2.6'
-      template = klass.new template, trim_mode: '-', eoutvar: erbout
-    else
-      template = klass.new template, nil, '-', erbout
-    end
+    template = klass.new template, trim_mode: '-', eoutvar: erbout
     @template_cache[file] = template
     template
   end