Found with bin/find-unneeded-includes
Only removal proposals are dealt with here.

Clean remaining cxx files in directories:
dif/ ftools/ html/ lotus/ orcus/ qpro/ rtf/ xcl97/

Change-Id: I219b61c087c07b0538b4525bf53d79f413d409c5
Reviewed-on: https://gerrit.libreoffice.org/66657
Tested-by: Jenkins
Reviewed-by: Miklos Vajna <vmiklos@collabora.com>