Revert "[docs] Add support for Markdown documentation in Sphinx"

The buildbots have an old version of Sphinx (need at least 1.3).  Revert until they are upgraded.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@337513 91177308-0d34-0410-b5e6-96231b3b80d8
3 files changed