Revert "[NFC][RemoveDIs] Bulk update utilities to insert with iterators"
This reverts commit 3fda50d3915b2163a54a37b602be7783a89dd808.
Apparently I've missed a hunk while staging this; will back out for now.
Picked up here: https://lab.llvm.org/buildbot/#/builders/139/builds/60429/steps/6/logs/stdio