packages: remove support for documentation on target

This patch removes deprecated symbol BR2_HAVE_DOCUMENTATION and all its
usage. Additionally, it removes the now unused BR2_DEPRECATED_SINCE_2012_11.

Signed-off-by: Thomas De Schampheleire <thomas.de.schampheleire@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>