[ruby/fileutils] Removed code for dead versions

https://github.com/ruby/fileutils/commit/1f707d8cc6

lib/fileutils.rb

@@ -837,13 +837,8 @@ module FileUtils
   def compare_stream(a, b)
     bsize = fu_stream_blksize(a, b)
 
-    if RUBY_VERSION > "2.4"
     sa = String.new(capacity: bsize)
     sb = String.new(capacity: bsize)
-    else
-      sa = String.new
-      sb = String.new
-    end
 
     begin
       a.read(bsize, sa)
@@ -1292,12 +1287,7 @@ module FileUtils
       opts = {}
       opts[:encoding] = fu_windows? ? ::Encoding::UTF_8 : path.encoding
 
-      files = if Dir.respond_to?(:children)
-        Dir.children(path, **opts)
-      else
-        Dir.entries(path(), **opts)
-           .reject {|n| n == '.' or n == '..' }
-      end
+      files = Dir.children(path, **opts)
 
       untaint = RUBY_VERSION < '2.7'
       files.map {|n| Entry_.new(prefix(), join(rel(), untaint ? n.untaint : n)) }