org.el (org-mode): Don't modify syntax entry for "@" globally

* lisp/org.el (org-mode): Don't modify syntax entry for "@" globally.

This syntax entry dates from commit fe939ecb when it was used to allow
"@" in tags.   Now "@" is a word constituent in tags, not anywhere.

lisp/org.el

@@ -5432,7 +5432,6 @@ The following commands are available:
   ;; Calc embedded
   (setq-local calc-embedded-open-mode "# ")
   ;; Modify a few syntax entries
-  (modify-syntax-entry ?@ "w")
   (modify-syntax-entry ?\" "\"")
   (modify-syntax-entry ?\\ "_")
   (modify-syntax-entry ?~ "_")