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

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

Change-Id: I6fe424e70baf844f10d918c3e399715aac99c00f
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>