Tune Tramp syntax

Tune Tramp syntax

* lisp/net/tramp-cmds.el (tramp-change-syntax):
Use `tramp-syntax-values'.

* lisp/net/tramp-compat.el (tramp-compat-tramp-syntax): New defsubst.

* lisp/net/tramp.el (tramp-syntax): Rename possible values.
(tramp-syntax-values): New defun.
(tramp-prefix-format, tramp-method-regexp)
(tramp-postfix-method-format, tramp-prefix-ipv6-format)
(tramp-postfix-ipv6-format, tramp-postfix-host-format)
(tramp-completion-file-name-regexp): Use `tramp-compat-tramp-syntax'
and changed values.
(tramp-completion-file-name-regexp-default): Rename from
`tramp-completion-file-name-regexp-unified'.  Adapt docstring.
(tramp-completion-file-name-regexp-simplified): Rename from
`tramp-completion-file-name-regexp-old-style'.  Adapt docstring.
(tramp-initial-completion-file-name-regexp):
Use `tramp-completion-file-name-regexp-default'.
(tramp-run-real-handler): Do not autoload any longer.