Remove old kickstart docs

doc/kickstart.txt

@@ -1,24 +0,0 @@
-================================================================================
-INTRODUCTION                                                  *kickstart.nvim*
-
-Kickstart.nvim is a project to help you get started on your neovim journey.
-
-                                                            *kickstart-is-not*
-It is not:
-- Complete framework for every plugin under the sun
-- Place to add every plugin that could ever be useful
-
-                                                                *kickstart-is*
-It is:
-- Somewhere that has a good start for the most common "IDE" type features:
-    - autocompletion
-    - goto-definition
-    - find references
-    - fuzzy finding
-    - and hinting at what more can be done :)
-- A place to _kickstart_ your journey.
-    - You should fork this project and use/modify it so that it matches your
-      style and preferences. If you don't want to do that, there are probably
-      other projects that would fit much better for you (and that's great!)!
-
- vim:tw=78:ts=8:ft=help:norl: