hidl_vec::iter: don't inherit from std::iterator am: 3197026bd4 am: 06da53dfb7

Original change: https://android-review.googlesource.com/c/platform/system/libhidl/+/3038265

Change-Id: I21955c18f85b2136f93b6abeaa0419350f84804e
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>