(perf): Deprecate link :outline properties

As it happens, turning sexps into strings is one of the
computationally expensive steps in EmacSQL.

With an enormous number of links in the database, that's a lot
of (:outline nil) to stringify into "(:outline nil)".

Its only use was in org-roam-node-insert-section,
where the information is very cheap to reconstruct.
It's already in one of the other arguments!

This has passed unnoticed because org-roam-db-sync has other
performance tarpits, but it will probably be noticed eventually after
those get fixed.

org-roam-db.el

@@ -108,7 +108,7 @@ ROAM_REFS."
   :type '(alist))
 
 ;;; Variables
-(defconst org-roam-db-version 18)
+(defconst org-roam-db-version 19)
 
 (defvar org-roam-db--connection (make-hash-table :test #'equal)
   "Database connection to Org-roam database.")
@@ -214,7 +214,7 @@ The query is expected to be able to fail, in this situation, run HANDLER."
        (source :not-null)
        (dest :not-null)
        (type :not-null)
-       (properties :not-null)]
+       properties]
       (:foreign-key [source] :references nodes [id] :on-delete :cascade)))))
 
 (defconst org-roam-db--table-indices
@@ -507,11 +507,8 @@ INFO is the org-element parsed buffer."
            (path (if (not option) path
                    (substring path 0 (match-beginning 0))))
            (source (org-roam-id-at-point))
-           (properties (list :outline (ignore-errors
-                                        ;; This can error if link is not under any headline
-                                        (org-get-outline-path 'with-self 'use-cache))))
-           (properties (if option (plist-put properties :search-option option)
-                         properties)))
+           (properties (when option
+                         (list :search-option option))))
       ;; For Org-ref links, we need to split the path into the cite keys
       (when (and source path)
         (if (and (boundp 'org-ref-cite-types)
@@ -533,9 +530,7 @@ INFO is the org-element parsed buffer."
     (goto-char (org-element-property :begin citation))
     (let ((key (org-element-property :key citation))
           (source (org-roam-id-at-point))
-          (properties (list :outline (ignore-errors
-                                       ;; This can error if link is not under any headline
-                                       (org-get-outline-path 'with-self 'use-cache)))))
+          (properties nil))
       (when (and source key)
         (org-roam-db-query
          [:insert :into citations