Remove some apostrophes from comments to work around puppet-mode bug.

The Emacs puppet-mode misinterprets apostrophes in comments and think
they are string quotes.  This breaks end-of-defun (C-M-e).  By not
having unmatched apostrophes in comments in class and define bodies,
we work around that.

This also fixes a genuine misspelling ("it's" instead of "its").

This was originally commit 028ff3e2716c in nsc-puppet-utils.