remove third-party libraries

Remove the bundled third-party libraries `tablist.el` and
`tablist-filter.el`.  Since the package `tablist` is available from
Melpa and therefore easy to install, there is no good reason to bundle
these libraries.  On the other hand bundling these libraries can cause
issues for people who install packages using Git submodules and might
then end up your potentially outdated copies instead of those from the
`tablist` submodule.  Possibly without noticing it.