(PUP-3229) Remove deprecate methods in BaseSetting class

In Puppet::Settings::BaseSetting, the following 4 methods were deprecated
long ago. This commit removes them:
call_on_define
call_on_define=
setbycli
setbycli=

This commit also makes a one-line change in call_hook= to remove an
unneeded conditional assignment (value can't have been assigned since
the value.nil? check two lines above).