remove: finally drop yum/repos.py and yum/yumRepo.py
:tests :move test_yumbase.py -> test_base.py
Filter rpm.RPMPROB_FILTER_OLDPACKAGE for all transactions whatsover (RhBug:916657)

IOW, if libsolv decides something is good to download, do not let rpm interfere.

Gets rid of tsInfo.probFilterFlags, replaces them with base-global
rpm_probfilter.