[CrOS Printing] Cleanup cups_ipp_util.h

Hide functions that aren't used outside of cups_ipp_util.cc

Bug: 964948
Change-Id: I31f6f41983827f5650a5a19b009bf0be1378efe2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1706521
Reviewed-by: Sean Kau <skau@chromium.org>
Commit-Queue: Vladislav Kuzkokov <vkuzkokov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#678636}
2 files changed