Remove DocumentDebugInfo as it's unused

In coverage dashboards this file shows up as 0%, however, it's
not being used. Coverage is a stage gate to board the mainline
train (and it's currently under the threshold) so ensuring our
coverage is highest is imperative.

Bug: 395926758
Test: Ensure DocsUI builds
Flag: EXEMPT Removing unused file
Change-Id: I12f17bccacf2be906020554ed530774a8315f560