cmake-mode.el: Simplify jumping to begin/end of functions/macros

This change was spawned by the desire to use `narrow-to-defun` in CMake
files. However, there was no "CMake version" of that function, and it
turns out that we don't need one if we make `beginning-of-defun` and
`end-of-defun` work in `cmake-mode`.

In the setup code of `cmake-mode` we now set the local variables
`beginning-of-defun-function` and `end-of-defun-function`. This makes
`beginning-of-defun` and `end-of-defun` work as expected.

Functions that use this facility also work now: `mark-defun` and
`narrow-to-defun` and possibly others.

We remove `cmake-mark-defun` since it's superfluous now.

We remove the defun-related key bindings since the standard functions
that are bound globally work fine with this patch.

Auxiliary/cmake-mode.el

@@ -258,15 +258,6 @@ Return t unless search stops due to end of buffer."
       (forward-line)
       t)))
 
-(defun cmake-mark-defun ()
-  "Mark the current CMake function or macro.
-
-This puts the mark at the end, and point at the beginning."
-  (interactive)
-  (cmake-end-of-defun)
-  (push-mark nil :nomsg :activate)
-  (cmake-beginning-of-defun))
-
 
 ;------------------------------------------------------------------------------
 
@@ -346,6 +337,10 @@ This puts the mark at the end, and point at the beginning."
 (define-derived-mode cmake-mode prog-mode "CMake"
   "Major mode for editing CMake source files."
 
+  ;; Setup jumping to beginning/end of a CMake function/macro.
+  (set (make-local-variable 'beginning-of-defun-function) #'cmake-beginning-of-defun)
+  (set (make-local-variable 'end-of-defun-function) #'cmake-end-of-defun)
+
   ; Setup font-lock mode.
   (set (make-local-variable 'font-lock-defaults) '(cmake-font-lock-keywords))
   ; Setup indentation function.
@@ -356,11 +351,6 @@ This puts the mark at the end, and point at the beginning."
   (set (make-local-variable 'syntax-propertize-function) cmake--syntax-propertize-function)
   (add-hook 'syntax-propertize-extend-region-functions #'syntax-propertize-multiline nil t))
 
-;; Default cmake-mode key bindings
-(define-key cmake-mode-map "\e\C-a" #'cmake-beginning-of-defun)
-(define-key cmake-mode-map "\e\C-e" #'cmake-end-of-defun)
-(define-key cmake-mode-map "\e\C-h" #'cmake-mark-defun)
-
 
 ; Help mode starts here