Skip post-minibuffer restore in erc-scrolltobottom-all

Skip post-minibuffer restore in erc-scrolltobottom-all

* etc/ERC-NEWS: Remove mention of `erc-scrolltobottom-relaxed' in
entry for module `scrolltobottom'.
* lisp/erc/erc-goodies.el (erc-input-line-position): Fix mention of
abandoned option `erc-scrolltobottom-relaxed'.
(erc-scrolltobottom-all): Subsume option `erc-scrolltobottom-relaxed'
by recognizing a third value state, `relaxed'.  A separate option
would make more sense if other options also depended on
`erc-scrolltobottom-all'.
(erc-scrolltobottom-relaxed): Remove redundant option, which was to be
new in ERC 5.6.
(erc-scrolltobottom-enable, erc-scrolltobottom-mode): Warn if user
attempts to enable `erc-scrolltobottom-all' on Emacs 27, which is not
supported.
(erc--scrolltobottom-relaxed-commands,
erc--scrolltobottom-post-force-commands,
erc--scrolltobottom-relaxed-skip-commands): Remove unused variables.
(erc--scrolltobottom-on-pre-command,
erc--scrolltobottom-on-pre-command-relaxed,
erc--scrolltobottom-on-post-command-relaxed): Remove unused functions.
(erc--scrolltobottom-on-post-command): Remove conditional branch for
dealing with a non-nil `erc--scrolltobottom-window-info'.
(erc--scrolltobottom-setup): Convert from generic to normal function
and remove setup and teardown for unused hooks.  Set variable
`read-minibuffer-restore-windows' locally when option
`erc-scrolltobottom-all' is non-nil.
(erc--scrolltobottom-on-pre-insert): Replace reference to subsumed
option `erc-scrolltobottom-relaxed' with new value `relaxed' for
existing option `erc-scrolltobottom-all'.
* test/lisp/erc/erc-scenarios-scrolltobottom-relaxed.el
(erc-scenarios-scrolltobottom--relaxed): Replace option
`erc-scrolltobottom-relaxed' with new value `relaxed' for
`erc-scrolltobottom-all'.  (Bug#64855)