Rename erc-server-buffer-p

Rename erc-server-buffer-p

* lisp/erc/erc-log.el (erc-log-all-but-server-buffers): Use
`erc--server-buffer-p' instead of `erc-server-buffer-p'.  This
replacement is presumed to be relatively "safe" because this function
is unused in the code base and only appears in the doc string for the
option `erc-enable-logging'.
* lisp/erc/erc-match.el (erc-match-message): Leave comment proposing
that `erc--server-buffer-p' should be preferred to
`erc-server-buffer-p'.  Use preferred alias for `erc-server-buffer-p'.
* lisp/erc/erc-notify.el (erc-cmd-NOTIFY): Use preferred alias for
`erc-server-buffer-p', and leave FIXME comment.
* lisp/erc/erc-speedbar.el (erc-speedbar-buttons): Use
`erc--server-buffer-p' instead of `erc-server-buffer-p'.  The logic
here seems simple enough to justify a change, however the absence of
related bug reports is perhaps an argument against this.
* lisp/erc/erc-track.el (erc-track-modified-channels): Use preferred
alias for `erc-server-buffer-p' and leave comment noting possible bug.
* lisp/erc/erc.el (erc-once-with-server-event): Use
`erc--server-buffer-p' instead of `erc-server-buffer-p'.  This change
seems justified because the function sets local hooks that would
otherwise be ignored outside of a server buffer.
(erc-server-buffer-p, erc-server-or-unjoined-channel-buffer-p): Make
the former an obsolete alias for the latter.
(erc--server-buffer-p): New function to replace `erc-server-buffer-p'
internally in new code.  Unlike its predecessor, it returns nil in
parted and kicked channels.
(erc-open-server-buffer-p): Use `erc--server-buffer-p' instead of
`erc-server-buffer-p'.  Given the name and the doc string, breaking
the odd misuse of this function in parted buffers seems justified
because this is clearly a bug fix.  Also, all uses in-tree conform to
the intended behavior as documented.  And a cursory grep of all "erc-"
prefixed packages on MELPA reveals zero instances of this function.
Nor is it used in erbot.
(erc-get-buffer): Mention behavior in doc string regarding parted and
kicked-from channels.
(erc-cmd-GQUIT): Fix wrong-number-of-arguments bug in timer function.
(erc-default-target): Mention behavior regarding unjoined channels.
(erc-kill-query-buffers): Don't use `erc-server-buffer-p'.  This
replacement may break third-party code expecting to leave parted
channels behind, but it seems sane when considering only the lone
internal use in `erc-cmd-QUIT'.
; * test/lisp/erc/resources/join/network-id/foonet.eld: Timeouts.
(Bug#66578)