Move :tools fly{check,spell} to :checkers {syntax,spell}

These modules were renamed so we can later generalize their
implementations, such as adding flymake support to the syntax checker.

core/core-modules.el

@@ -24,7 +24,9 @@
               (debugger (:tools debugger)))
     (:tools (rotate-text (:editor rotate-text))
             (vterm (:term vterm))
-            (password-store (:tools pass)))
+            (password-store (:tools pass))
+            (flycheck (:checker syntax))
+            (flyspell (:checker spell)))
     (:emacs (electric-indent (:emacs electric))
             (hideshow (:editor fold))
             (eshell (:term eshell))