cmake-mode.el: Avoid using beginning-of-buffer

This should not be used from lisp programs.  Use the replacement
suggested by the doc: (goto-char (point-min))
cmake-mode.el: Don't assign to free variable save-point

Drop use of the free variable from unscreamify-cmake-buffer.

The proper way to do this would be defvar or let, but it is more
sensible to drop the feature completely: replace-match will shift the
point and the saved-point will be invalid. More careful coding could
avoid this, but seems overkill.
cmake-mode.el: Replace 'setq' with 'let' or inlining
Merge topic 'emacs-mode-byte-compile' into next

9b3876bf cmake-mode.el: Replace 'setq' with 'let' or inlining
d3db7126 cmake-mode.el: Don't assign to free variable save-point
fbc3a6f3 cmake-mode.el: Avoid using beginning-of-buffer