bug#50245: 28.0.50; Instrumenting a function does not show "Edebug:" in the echo area

[Lars Ingebrigtsen]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

> What makes us think that `edebug-all-defs` will always be defined when
> we get here?  Doesn't this code signal an error if called before
> edebug.el is loaded (e.g. in the case of `emacs -Q` soon followed by
> a plain `C-M-x`)?

edebug-all-defs is autoloaded, so it's safe to use here (and the (defvar
isn't needed, so I removed it).