Temporarily revert "[Attributor] Unify testing (=updates,...)"

This patch reverts the 2 patches below, as on most systems the disabled
tests actually pass and that causes most bots to be red, including
  http://green.lab.llvm.org/green/job/clang-stage1-RA/8541/
  http://green.lab.llvm.org/green/job/clang-stage1-cmake-RA-expensive/15646/
  http://lab.llvm.org:8011/builders/clang-ppc64le-linux-lnt/builds/23690
  http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux-bootstrap/builds/16751

* [Attributor] Disable three tests until the SCC update bug was fixed
  commit 2ae1a76c.

* [Attributor] Unify testing (=updates,prefixes,run configurations,...)
  2bcf5793.