harmonize copy ctor and asignment op for etl::delegate (#465)
harmonize copy ctor and asignment op for etl::delegate (#465)

etl::delegate has a user-written copy constructor and a defaulted assignment
operator. The copy constructor does the same as a defaulted copy constructor,
therefore there is no need to add a user-written copy constructor.

The combination of user-written copy constructor and defaulted assignment
operator causes a warning in Coverity, a static code analyzer:

copy_without_assign: Class etl::delegate<void ()> has a user-written copy constructor etl::delegate<void ()>::delegate(etl::delegate<void ()> const &) but no corresponding user-written assignment operator.

This commit replaces the user-written copy constructor with a defaulted copy
constructor, which does the same.
ETLCPP/etl,ETLCPP/etl,ETLCPP/etl,ETLCPP/etl