systemc: replace the deprecated std::iterator

std::iterator is deprecated in c++17. We can just declare the
required types for iterator traits directly without the helper.

Change-Id: I789e2c2b13e56cc391527686109df8b779474d09
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/66351
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed