cppcms: really depend on wchar

In commit f8993ebb ("cppcms: needs
wchar support even without icu"), Peter wanted to move the wchar
dependency from the ICU sub-option of cppcms to the main cppcms option
itself. However, for some reason it didn't do the entire change, and
the commit was lacking:

 * Removing the wchar dependency from BR2_PACKAGE_CPPCMS_ICU

 * Adding the wchar dependency to BR2_PACKAGE_CPPCMS.

It was only handling the two comments.

This should really fix:

  http://autobuild.buildroot.net/results/6f8/6f8e8b68235f6cf0dfef13e3ed11f97a3ab50a06/



and other similar build failures that are still occuring after
f8993ebb has been applied.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>