22318: Remove obsolete checks from run-tests

22318: Remove obsolete checks from run-tests

* gnutls.h: You need a TLS backend for curl, but the specific one
  doesn't matter. We already check for curl; the odds that the user
  installed one without TLS are near-zero (Debian doesn't package
  one by itself).

* libattr1: This used to be required for llfuse (required by
  services/fuse), but they have since switched to sys/xattr.h
  provided by glibc.

* graphviz: Used to be required by Workbench 1.

* pandoc: I guess this was required to generate R SDK documentation,
  but it isn't anymore.

Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith@curii.com>