test_in_tail: Simplify cleanup_directory and cleanup_file

Since we always create a new test ditectory on each tests, ensuring to
remove old directory in hacky way is no longer needed.
In addition, we already dropped Ruby 2.6 support, and the previous
implementation has some bugs. For example `FileUtils.rm_f` doesn't
have `secure` option even though the latest Ruby (v3.1), probably it
intend `FileUtils.rm_r`.

Signed-off-by: Takuro Ashie <ashie@clear-code.com>

test/plugin/test_in_tail.rb

@@ -31,60 +31,11 @@ def cleanup_directory(path)
       return
     end
 
-    if Fluent.windows?
-      Dir.glob("*", base: path).each do |name|
-        begin
-          cleanup_file(File.join(path, name))
-        rescue
-          # expect test driver block release already owned file handle.
-        end
-      end
-    else
-      begin
-        FileUtils.rm_f(path, secure:true)
-      rescue ArgumentError
-        FileUtils.rm_f(path) # For Ruby 2.6 or before.
-      end
-      if File.exist?(path)
-        FileUtils.remove_entry_secure(path, true)
-      end
-    end
-    FileUtils.mkdir_p(path)
+    FileUtils.remove_entry_secure(path, true)
   end
 
   def cleanup_file(path)
-    if Fluent.windows?
-      # On Windows, when the file or directory is removed and created
-      # frequently, there is a case that creating file or directory will
-      # fail. This situation is caused by pending file or directory
-      # deletion which is mentioned on win32 API document [1]
-      # As a workaround, execute rename and remove method.
-      #
-      # [1] https://docs.microsoft.com/en-us/windows/win32/api/fileapi/nf-fileapi-createfilea#files
-      #
-      file = File.join(Dir.tmpdir, SecureRandom.hex(10))
-      begin
-        FileUtils.mv(path, file)
-        FileUtils.rm_rf(file, secure: true)
-      rescue ArgumentError
-        FileUtils.rm_rf(file) # For Ruby 2.6 or before.
-      end
-      if File.exist?(file)
-        # ensure files are closed for Windows, on which deleted files
-        # are still visible from filesystem
-        GC.start(full_mark: true, immediate_mark: true, immediate_sweep: true)
-        FileUtils.remove_entry_secure(file, true)
-      end
-    else
-      begin
-        FileUtils.rm_f(path, secure: true)
-      rescue ArgumentError
-        FileUtils.rm_f(path) # For Ruby 2.6 or before.
-      end
-      if File.exist?(path)
-        FileUtils.remove_entry_secure(path, true)
-      end
-    end
+    FileUtils.remove_entry_secure(path, true)
   end
 
   def create_target_info(path)