options DOCS + EXAMPLES

[Harry Schmalzbauer]

Hello,

found out that the need to define DOCS and EXAMPLES in OPTIONS_DEFINE 
was made mandatory some time ago, which ports-mgmt/portlint isn't aware 
about yet (found https://reviews.freebsd.org/D13036).

I intentionally haven't defined it, because I want to make use of the 
bsd.ports.mk handling of PORTDOCS and PORTEXAMPLES, but don't want to 
spam the UI.  EXAMPLES and DOCS shall stay mandatory for my port, as 
long as the user changes the corresponding defaults.

How do I hide the user selection for EXAMPLES and DOCS after the change 
(which I wasn't able to find by reading commit logs)?

Thanks,

-harry