Revert aa89c84e00d8dc85100e6fedab7631c415e6364d (bug#38457)

Revert aa89c84e00d8dc85100e6fedab7631c415e6364d (bug#38457)

* src/editfns.c (Fmessage): Don't use minibuffer-message.
(Fmessage_in_echo_area): Remove function message-in-echo-area.
(syms_of_editfns): Remove variable message-in-echo-area.

* lisp/isearch.el (isearch--momentary-message): Remove message-in-echo-area.
* lisp/minibuffer.el (minibuffer-message): Don't record message
in the *Messages* buffer.
(minibuffer-completion-help): Remove message-in-echo-area.

* lisp/subr.el (do-after-load-evaluation): Remove discard-input (bug#38560)