ox-beamer: Small clean-up

* lisp/ox-beamer.el: Remove unnecessary package definitions in default
  class.

lisp/ox-beamer.el

@@ -36,10 +36,7 @@
 (unless (assoc "beamer" org-latex-classes)
   (add-to-list 'org-latex-classes
 	       '("beamer"
-		 "\\documentclass[presentation]{beamer}
-\[DEFAULT-PACKAGES]
-\[PACKAGES]
-\[EXTRA]"
+		 "\\documentclass[presentation]{beamer}"
 		 ("\\section{%s}" . "\\section*{%s}")
 		 ("\\subsection{%s}" . "\\subsection*{%s}")
 		 ("\\subsubsection{%s}" . "\\subsubsection*{%s}"))))