Refactor core-ui

+ Remove doom/switch-theme (replaced with an advice for load-theme)
+ Reorganize core-ui
+ Fix Emacs 26+ hl-line hack being applied for Emacs 25 users
+ Rename doom|show-whitespace-maybe to doom|highlight-non-default-indentation
+ Disable tool-bar, menu-bar and vertical-scroll-bars via
  default-frame-alist; this is a little faster than using the minor
  modes.

core/autoload/buffers.el

@@ -199,18 +199,6 @@ regex PATTERN. Returns the number of killed buffers."
 ;; Hooks
 ;;
 
-;;;###autoload
-(defun doom|protect-visible-buffer ()
-  "Don't kill the current buffer if it is visible in another window (bury it
-instead). Meant for `kill-buffer-query-functions'."
-  (not (and (delq (selected-window) (get-buffer-window-list nil nil t))
-            (not (member (substring (buffer-name) 0 1) '(" " "*"))))))
-
-;;;###autoload
-(defun doom|protect-fallback-buffer ()
-  "Don't kill the scratch buffer. Meant for `kill-buffer-query-functions'."
-  (not (eq (current-buffer) (doom-fallback-buffer))))
-
 ;;;###autoload
 (defun doom|mark-buffer-as-real ()
   "Hook function that marks the current buffer as real."

core/autoload/ui.el

@@ -113,23 +113,6 @@ presentations."
     (doom|init-theme)
     (doom|init-fonts)))
 
-;;;###autoload
-(defun doom/switch-theme (theme)
-  "Like `load-theme', but will unload currently loaded themes before switching
-to a new one."
-  (interactive
-   (list (completing-read
-          "Load theme: "
-          (mapcar #'symbol-name
-                  (custom-available-themes)))))
-  (condition-case nil
-      (progn
-        (mapc #'disable-theme custom-enabled-themes)
-        (load-theme (intern theme) t)
-        (when (fboundp 'powerline-reset)
-          (powerline-reset)))
-    (error "Problem loading theme %s" x)))
-
 ;;;###autoload
 (defun doom*recenter (&rest _)
   (recenter))