Backport commit 542443645 from Emacs

* lisp/org-id.el (org-id-link-to-org-use-id):
* lisp/org.el (org-support-shift-select, org-file-apps):
Remove backslash-newline that immediately precedes another
newline, as this is not the usual style and is confusing.

Avoid backslash-newline-newline in source code
5424436452bc0b3d8a62a8398f92d0c2db81e22b
Paul Eggert
Wed May 22 23:59:36 2019 -0700

lisp/org-id.el

@@ -84,8 +84,7 @@
 
 (defcustom org-id-link-to-org-use-id nil
   "Non-nil means storing a link to an Org file will use entry IDs.
-\\<org-mode-map>\
-
+\\<org-mode-map>
 The variable can have the following values:
 
 t     Create an ID if needed to make a link to the current entry.

lisp/org.el

@@ -907,8 +907,7 @@ depends on, if any."
 
 (defcustom org-support-shift-select nil
   "Non-nil means make shift-cursor commands select text when possible.
-\\<org-mode-map>\
-
+\\<org-mode-map>
 In Emacs 23, when `shift-select-mode' is on, shifted cursor keys
 start selecting a region, or enlarge regions started in this way.
 In Org mode, in special contexts, these same keys are used for
@@ -2284,8 +2283,7 @@ See `org-file-apps'.")
     ("\\.x?html?\\'" . default)
     ("\\.pdf\\'" . default))
   "External applications for opening `file:path' items in a document.
-\\<org-mode-map>\
-
+\\<org-mode-map>
 Org mode uses system defaults for different file types, but
 you can use this variable to set the application for a given file
 extension.  The entries in this list are cons cells where the car identifies