(python-mode-map): Use abbrev-table-menu.

(python-mode-map): Use abbrev-table-menu.
(python-use-skeletons): Remove, unused.
(python-skeletons): Remove.  Use the abbrev table instead.
(python-mode-abbrev-table): Fix regexp; add enable-function and case-fixed.
(def-python-skeleton): Simplify.
(python-expand-template): Use the abbrev-table and abbrev-insert.
(python-abbrev-pc-hook, python-abbrev-syntax-table, python-pea-hook): Remove.
(python-mode): Don't set pre-abbrev-expand-hook.