Don't install libomp -- we'll see if d951c6a is still relevant

Author: ldionne

libcxx/utils/ci/docker/linux-builder-base.dockerfile

@@ -116,7 +116,6 @@ RUN <<EOF
   sudo /tmp/llvm.sh $(($LLVM_HEAD_VERSION - 2)) all  # previous release
   sudo /tmp/llvm.sh $(($LLVM_HEAD_VERSION - 1)) all  # latest release
   sudo /tmp/llvm.sh $LLVM_HEAD_VERSION          all  # current ToT
-  sudo apt-get install -y libomp5-$LLVM_HEAD_VERSION
   sudo rm -rf /var/lib/apt/lists/*
 EOF