QFlags<>: let the compiler generate copy ctor/op=

QFlags<>: let the compiler generate copy ctor/op=

The user-defined copy constructor and
copy-assignment operators were 100% equivalent
to the ones the compiler would generate, so
let the compiler generate them (so we reap
move constructors, too, even though they're
not needed on this class).

Change-Id: Iecdd579fa5a819d083ec9b2f25734ddba85515e6
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>