Delete layer evil-cleverparens and move the package to spacemacs-evil layer.
The feature is called "Safe structurral editing" for lisp dialects. Support for
it is added via pre-init functions in each of the concerned layer and proper
documentation is added to their README.org files.
This also removes the recently added package evil-smartparens. The goal is
to choose the best package for evil safe structural editing. For now we use
evil-cleverparens as we supported it first, if evil-smartparens is shown to be
a better package we will be able to switch to it.
