revert: fix(docs): set mode in file-local vars

emacs-straight/org-mode@e22b4eb7aa introduced a breaking change that
made it impossible to rely on .dir-locals.el to change org-mode buffers
in $EMACSDIR to doom-docs-org-mode (without infinite recursion), so we
used file-local variables in 7e400ab.

emacs-straight/org-mode@215de6176b reverted that change, so we can use
.dir-locals.el again, and this is my preference, since it requires less
boilerplate across our hundreds of org files.

Ref: emacs-straight/org-mode@215de6176b
Ref: emacs-straight/org-mode@e22b4eb7aa
Revert: 7e400abdc0

modules/editor/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:   :editor
 #+created: July 30, 2021
 #+since:   21.12.0

modules/editor/evil/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor evil
 #+subtitle: The text editor Emacs was missing
 #+created:  April 08, 2020

modules/editor/file-templates/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor file-templates
 #+subtitle: Fill the void in your empty files
 #+created:  February 11, 2017

modules/editor/file-templates/templates/org-mode/__doom-category-readme

@@ -1,7 +1,6 @@
 # -*- mode: snippet -*-
 # name: Doom category readme
 # --
-# -*- mode: doom-docs-org -*-
 :PROPERTIES:
 :ID:       `(doom-docs-generate-id)`
 :END:

modules/editor/file-templates/templates/org-mode/__doom-docs

@@ -1,7 +1,6 @@
 # -*- mode: snippet -*-
 # name: Doom documentation
 # --
-# -*- mode: doom-docs-org -*-
 :PROPERTIES:
 :ID:       `(doom-docs-generate-id)`
 :END:

modules/editor/file-templates/templates/org-mode/__doom-readme

@@ -1,7 +1,6 @@
 # -*- mode: snippet -*-
 # name: Doom module readme                                             
 # --
-# -*- mode: doom-docs-org -*-
 :PROPERTIES:
 :ID:       `(doom-docs-generate-id)`
 :END:

modules/editor/fold/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor fold
 #+subtitle: What you can't see won't hurt you
 #+created:  May 15, 2019

modules/editor/format/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor format
 #+subtitle: Standardize your ugly code
 #+created:  July 26, 2020

modules/editor/god/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor god
 #+subtitle: IDDQD
 #+created:  October 13, 2021

modules/editor/lispy/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor lispy
 #+subtitle: Vim for lisp, for people who don't like vim
 #+created:  October 27, 2018

modules/editor/multiple-cursors/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor multiple-cursors
 #+subtitle: Make all your mistakes at once
 #+created:  October 13, 2021

modules/editor/objed/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor objed
 #+subtitle: Text object editing for the innocent
 #+created:  May 30, 2019

modules/editor/parinfer/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor parinfer
 #+subtitle: For lispers that like Python more (i.e. nobody)
 #+created:  February 27, 2021

modules/editor/rotate-text/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor rotate-text
 #+subtitle: The only back'n'forth nerds will ever know
 #+created:  June 22, 2018

modules/editor/snippets/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor snippets
 #+subtitle: My elves type so I don't have to
 #+created:  February 11, 2017

modules/editor/word-wrap/README.org

@@ -1,4 +1,3 @@
-# -*- mode: doom-docs-org -*-
 #+title:    :editor word-wrap
 #+subtitle: Soft-wrapping with language-aware indent
 #+created:  August 25, 2019