Require less packages in Tramp

Require less packages in Tramp

* lisp/net/tramp-compat.el (format-spec): Do not require advice, cl-lib,
custom, password-cache, timer and ucs-normalize.

* lisp/net/tramp-gvfs.el: Do not require zeroconf.  Declare
zeroconf-* functions.
(tramp-gvfs-enabled): Autoload `zeroconf-init'.

* lisp/net/tramp-sh.el: Do not require dired.

* lisp/net/tramp.el (tramp-get-debug-buffer): Do not require outline.
(tramp-file-name-for-operation): Extend docstring.
(tramp-parse-netrc): Do not require netrc.  Autoload `netrc-parse'.