Run erc--scrolltobottom-on-pre-insert unconditionally

Run erc--scrolltobottom-on-pre-insert unconditionally

* lisp/erc/erc-goodies.el (erc--scrolltobottom-all): Pass `no-force'
argument to `set-window-start'.
(erc--scrolltobottom-on-pre-insert): Convert from generic to normal
function and drop `erc-input' method completely.  A non-nil `insertp'
slot means a message is marked for insertion in the read-only portion
of the buffer, above the prompt.  But conditionally restoring window
parameters based on that flag is insufficient because the window still
needs adjusting whenever input is typed, regardless of whether it's
erased or "inserted."  (Bug#64855)