rgw: remove noexcept from function definition

rgw: remove noexcept from function definition

Clang complains:
src/rgw/rgw_bucket_sync_cache.h:88:3: error: exception specification of explicitly defaulted copy co
nstructor does not match the calculated one
  Handle(const Handle&) noexcept = default;
  ^
1 error generated.

And a reference that I found for this:
    https://github.com/mapnik/mapnik/issues/3274
Suggesting that the noexcept is inherited from the first definition.

Signed-off-by: Willem Jan Withagen <wjw@digiware.nl>