Replace some uses of cl-mapcan with mapcan

* lisp/progmodes/project.el (project-files, project-files):
* lisp/progmodes/xref.el (xref-backend-references)
(xref--convert-hits):
* test/lisp/emacs-lisp/package-tests.el
(package-test-strip-version): Replace cl-mapcan with equivalent
calls to mapcan.

lisp/progmodes/project.el

@@ -195,7 +195,7 @@ subset of the project root and external roots.
 
 The default implementation uses `find-program'.  PROJECT is used
 to find the list of ignores for each directory."
-  (cl-mapcan
+  (mapcan
    (lambda (dir)
      (project--files-in-directory dir
                                   (project--dir-ignores project dir)))
@@ -351,7 +351,7 @@ backend implementation of `project-external-roots'.")
    (list (project-root project))))
 
 (cl-defmethod project-files ((project (head vc)) &optional dirs)
-  (cl-mapcan
+  (mapcan
    (lambda (dir)
      (let (backend)
        (if (and (file-equal-p dir (cdr project))

lisp/progmodes/xref.el

@@ -264,7 +264,7 @@ be found, return nil.
 The default implementation uses `semantic-symref-tool-alist' to
 find a search tool; by default, this uses \"find | grep\" in the
 `project-current' roots."
-  (cl-mapcan
+  (mapcan
    (lambda (dir)
      (xref-references-in-directory identifier dir))
    (let ((pr (project-current t)))
@@ -1383,8 +1383,8 @@ Such as the current syntax table and the applied syntax properties."
   (let (xref--last-file-buffer
         (tmp-buffer (generate-new-buffer " *xref-temp*")))
     (unwind-protect
-        (cl-mapcan (lambda (hit) (xref--collect-matches hit regexp tmp-buffer))
-                   hits)
+        (mapcan (lambda (hit) (xref--collect-matches hit regexp tmp-buffer))
+                hits)
       (kill-buffer tmp-buffer))))
 
 (defun xref--collect-matches (hit regexp tmp-buffer)

test/lisp/emacs-lisp/package-tests.el

@@ -175,9 +175,8 @@
 
 (defun package-test-suffix-matches (base suffix-list)
   "Return file names matching BASE concatenated with each item in SUFFIX-LIST"
-  (cl-mapcan
-   (lambda (item) (file-expand-wildcards (concat base item)))
-   suffix-list))
+  (mapcan (lambda (item) (file-expand-wildcards (concat base item)))
+          suffix-list))
 
 (defvar tar-parse-info)
 (declare-function tar-header-name "tar-mode" (cl-x) t) ; defstruct