Various dbus.el cleanups (bug#41744)

Various dbus.el cleanups (bug#41744)

* etc/NEWS: Announce removal of aliases obsolete since Emacs 24.3.

* lisp/net/dbus.el: Remove unneeded dependency on cl-lib.el.  Quote
function symbols as such.
(dbus-ignore-errors): Don't add macro name to font-lock keywords, as
emacs-lisp-mode now dynamically fontifies new macro definitions.
(dbus-event-error-hooks, dbus-call-method-non-blocking): Remove
aliases obsolete since Emacs 24.3.
(dbus-register-signal, dbus-escape-as-identifier): Simplify.  Use
regexp \` and \' in place of ^ and $.
(dbus--parse-xml-buffer): New function for libxml2 compatibility.
(dbus-introspect-xml): Use it.

(dbus-string-to-byte-array, dbus-byte-array-to-string)
(dbus-unescape-from-identifier, dbus-list-known-names)
(dbus-introspect-get-all-nodes, dbus-get-all-properties)
(dbus-get-all-managed-objects): Simplify.

(dbus--introspect-names, dbus--introspect-name): New convenience
functions.
(dbus-introspect-get-node-names)
(dbus-introspect-get-interface-names)
(dbus-introspect-get-interface, dbus-introspect-get-method-names)
(dbus-introspect-get-method, dbus-introspect-get-signal-names)
(dbus-introspect-get-signal, dbus-introspect-get-property-names)
(dbus-introspect-get-property)
(dbus-introspect-get-annotation-names)
(dbus-introspect-get-annotation)
(dbus-introspect-get-argument-names, dbus-introspect-get-argument):
Use them to DRY.

* test/lisp/net/dbus-tests.el (dbus-test-all): Quote function
symbols as such.