[lit] Remove LitTestCase

From the docs: `class LitTestCase(unittest.TestCase)`
LitTestCase is an adaptor for providing a 'unittest' compatible
interface to 'lit' tests so that we can run lit tests with standard
python test runners.

It does not seem to be used anywhere.

Differential Revision: https://reviews.llvm.org/D58264

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354188 91177308-0d34-0410-b5e6-96231b3b80d8
7 files changed