Remove OpenScop

We only supported a very old version of OpenScop that was entirely different
to what OpenScop is today. To not confuse people, we remove this old and
unusable support. If anyone is interested to add OpenScop support back in,
the relevant patches are available in version control.

git-svn-id: https://llvm.org/svn/llvm-project/polly/trunk@206026 91177308-0d34-0410-b5e6-96231b3b80d8