emacs: remove unnecessary notmuch-remove-if-not

We could just have switched to using `cl-remove-if-not' instead,
but the two uses of the *remove-if-not function are pretty strange
to begin with so we refactor to not use any such function at all.

emacs/notmuch-hello.el

@@ -21,8 +21,7 @@
 
 ;;; Code:
 
-(eval-when-compile (require 'cl-lib))
-
+(require 'cl-lib)
 (require 'widget)
 (require 'wid-edit) ; For `widget-forward'.
 
@@ -542,9 +541,7 @@ options will be handled as specified for
 --batch'. In general we recommend running matching versions of
 the CLI and emacs interface."))
     (goto-char (point-min))
-    (notmuch-remove-if-not
-     #'identity
-     (mapcar
+    (cl-mapcan
      (lambda (elem)
        (let* ((elem-plist (notmuch-hello-saved-search-to-plist elem))
 	      (search-query (plist-get elem-plist :query))
@@ -555,8 +552,8 @@ the CLI and emacs interface."))
 	 (when (and filtered-query (or (plist-get options :show-empty-searches)
 				       (> message-count 0)))
 	   (setq elem-plist (plist-put elem-plist :query filtered-query))
-	    (plist-put elem-plist :count message-count))))
-      query-list))))
+	   (list (plist-put elem-plist :count message-count)))))
+     query-list)))
 
 (defun notmuch-hello-insert-buttons (searches)
   "Insert buttons for SEARCHES.
@@ -698,12 +695,12 @@ Complete list of currently available key bindings:
 
 (defun notmuch-hello-generate-tag-alist (&optional hide-tags)
   "Return an alist from tags to queries to display in the all-tags section."
-  (mapcar (lambda (tag)
-	    (cons tag (concat "tag:" (notmuch-escape-boolean-term tag))))
-	  (notmuch-remove-if-not
-	   (lambda (tag)
-	     (not (member tag hide-tags)))
-	   (process-lines notmuch-command "search" "--output=tags" "*"))))
+  (cl-mapcan (lambda (tag)
+	       (and (not (member tag hide-tags))
+		    (list (cons tag
+				(concat "tag:"
+					(notmuch-escape-boolean-term tag))))))
+	     (process-lines notmuch-command "search" "--output=tags" "*")))
 
 (defun notmuch-hello-insert-header ()
   "Insert the default notmuch-hello header."

emacs/notmuch-lib.el

@@ -534,15 +534,6 @@ This replaces spaces, percents, and double quotes in STR with
 
 ;;
 
-(defun notmuch-remove-if-not (predicate list)
-  "Return a copy of LIST with all items not satisfying PREDICATE removed."
-  (let (out)
-    (while list
-      (when (funcall predicate (car list))
-	(push (car list) out))
-      (setq list (cdr list)))
-    (nreverse out)))
-
 (defun notmuch-plist-delete (plist property)
   (let* ((xplist (cons nil plist))
 	 (pred xplist))