wcn36xx: remove legacy code from Makefile

wcn36xx used to be built with android. Now we use backports so
there is no need in android related code.

Signed-off-by: Eugene Krasnikov <k.eugene.e@gmail.com>
wcn36xx: move all documentation to one place

Now all information about wcn36xx is concentrated in one
place: http://wireless.kernel.org/en/users/Drivers/wcn36xx

Signed-off-by: Eugene Krasnikov <k.eugene.e@gmail.com>