Refactor org-set-font-lock-defaults to improve code readability

* org.el (org-set-font-lock-defaults): Reduce number of local
variables to improve code readability.

lisp/org.el

@@ -5617,9 +5617,7 @@ needs to be inserted at a specific position in the font-lock sequence.")
 
 (defun org-set-font-lock-defaults ()
   "Set font lock defaults for the current buffer."
-  (let* ((em org-fontify-emphasized-text)
-	 (lk org-highlight-links)
-	 (org-font-lock-extra-keywords
+  (let ((org-font-lock-extra-keywords
 	  (list
 	   ;; Call the hook
 	   '(org-font-lock-hook)
@@ -5646,10 +5644,10 @@ needs to be inserted at a specific position in the font-lock sequence.")
 	   '(org-fontify-drawers)
 	   ;; Link related fontification.
 	   '(org-activate-links)
-	   (when (memq 'tag lk) '(org-activate-tags (1 'org-tag prepend)))
-	   (when (memq 'radio lk) '(org-activate-target-links (1 'org-link t)))
-	   (when (memq 'date lk) '(org-activate-dates (0 'org-date t)))
-	   (when (memq 'footnote lk) '(org-activate-footnote-links))
+	   (when (memq 'tag org-highlight-links) '(org-activate-tags (1 'org-tag prepend)))
+	   (when (memq 'radio org-highlight-links) '(org-activate-target-links (1 'org-link t)))
+	   (when (memq 'date org-highlight-links) '(org-activate-dates (0 'org-date t)))
+	   (when (memq 'footnote org-highlight-links) '(org-activate-footnote-links))
            ;; Targets.
            (list org-radio-target-regexp '(0 'org-target t))
 	   (list org-target-regexp '(0 'org-target t))
@@ -5693,7 +5691,7 @@ needs to be inserted at a specific position in the font-lock sequence.")
 	   (list (concat "\\<" org-closed-string) '(0 'org-special-keyword t))
 	   (list (concat "\\<" org-clock-string) '(0 'org-special-keyword t))
 	   ;; Emphasis
-	   (when em '(org-do-emphasis-faces))
+	   (when org-fontify-emphasized-text '(org-do-emphasis-faces))
 	   ;; Checkboxes
 	   '("^[ \t]*\\(?:[-+*]\\|[0-9]+[.)]\\)[ \t]+\\(?:\\[@\\(?:start:\\)?[0-9]+\\][ \t]*\\)?\\(\\[[- X]\\]\\)"
 	     1 'org-checkbox prepend)