Inline important-return-value declarations in cl-lib.el

These declarations are now properly added to 'cl-lib.el' itself, or to
'cl-loaddefs.el'.  This means that they will now correctly show up
immediately when loading 'cl-lib.el', instead of only after 'cl-macs.el'
is pulled in by an autoload.  C.f. Bug#76247.

I did not considered worth reproducing everywhere the list saying which
functions among the below belong to these two categories:
1. Functions that are side-effect-free except for the behavior of
   functions passed as argument.
2. Functions that mutate and return a list.

AFAIU, this is not actionable with our current byte-compiler, i.e. we
can't add any extra declarations based on it.  However, if the list
should be needed at some point, for example due to improvements in the
compiler, this commit will be where to find it.  In the worst case, and
with more work, it's also deducible from the source code itself.

* lisp/emacs-lisp/cl-macs.el: Move important-return-value declarations
from here...
* lisp/emacs-lisp/cl-extra.el (cl-map, cl-maplist, cl-mapcan)
(cl-mapcon, cl-some, cl-every, cl-notany, cl-notevery, cl-nreconc):
* lisp/emacs-lisp/cl-lib.el (cl-mapcar, cl-adjoin, cl-subst):
* lisp/emacs-lisp/cl-seq.el (cl-reduce, cl-remove, cl-remove-if)
(cl-remove-if-not, cl-delete, cl-delete-if, cl-delete-if-not)
(cl-remove-duplicates, cl-delete-duplicates, cl-substitute)
(cl-substitute-if, cl-substitute-if-not, cl-nsubstitute)
(cl-nsubstitute-if, cl-nsubstitute-if-not, cl-find, cl-find-if)
(cl-find-if-not, cl-position, cl-position-if, cl-position-if-not)
(cl-count, cl-count-if, cl-count-if-not, cl-mismatch, cl-search)
(cl-sort, cl-stable-sort, cl-merge, cl-member, cl-member-if)
(cl-member-if-not, cl-assoc, cl-assoc-if, cl-assoc-if-not, cl-rassoc)
(cl-rassoc-if, cl-rassoc-if-not, cl-union, cl-nunion, cl-intersection)
(cl-nintersection, cl-set-difference, cl-nset-difference)
(cl-set-exclusive-or, cl-nset-exclusive-or, cl-subsetp, cl-subst-if)
(cl-subst-if-not, cl-nsubst, cl-nsubst-if, cl-nsubst-if-not, cl-sublis)
(cl-nsublis, cl-tree-equal): ...to have them inline here.

lisp/emacs-lisp/cl-macs.el

@@ -3729,46 +3729,6 @@ macro that returns its `&whole' argument."
 (cl-proclaim '(inline cl-acons cl-map cl-notany cl-notevery cl-revappend
                cl-nreconc))
 
-
-;;; Things whose return value should probably be used.
-(mapc (lambda (x) (function-put x 'important-return-value t))
-       '(
-         ;; Functions that are side-effect-free except for the
-         ;; behavior of functions passed as argument.
-         cl-mapcar cl-mapcan cl-maplist cl-map cl-mapcon
-         cl-reduce
-         cl-assoc cl-assoc-if cl-assoc-if-not
-         cl-rassoc cl-rassoc-if cl-rassoc-if-not
-         cl-member cl-member-if cl-member-if-not
-         cl-adjoin
-         cl-mismatch cl-search
-         cl-find cl-find-if cl-find-if-not
-         cl-position cl-position-if cl-position-if-not
-         cl-count cl-count-if cl-count-if-not
-         cl-remove cl-remove-if cl-remove-if-not
-         cl-remove-duplicates
-         cl-subst cl-subst-if cl-subst-if-not
-         cl-substitute cl-substitute-if cl-substitute-if-not
-         cl-sublis
-         cl-union cl-intersection cl-set-difference cl-set-exclusive-or
-         cl-subsetp
-         cl-every cl-some cl-notevery cl-notany
-         cl-tree-equal
-
-         ;; Functions that mutate and return a list.
-         cl-delete cl-delete-if cl-delete-if-not
-         cl-delete-duplicates
-         cl-nsubst cl-nsubst-if cl-nsubst-if-not
-         cl-nsubstitute cl-nsubstitute-if cl-nsubstitute-if-not
-         cl-nunion cl-nintersection cl-nset-difference cl-nset-exclusive-or
-         cl-nreconc cl-nsublis
-         cl-merge
-         ;; It's safe to ignore the value of `cl-sort' and `cl-stable-sort'
-         ;; when used on arrays, but most calls pass lists.
-         cl-sort cl-stable-sort
-         ))
-
-
 ;;; Types and assertions.
 
 ;;;###autoload