Remove LLVM

doc/notebooks/demo_wave_equation.ipynb

pystencils/backends/__init__.py

pystencils/cpu/cpujit.py

pystencils/data_types.py

pystencils/enums.py

pystencils/kernelcreation.py

pystencils/llvm/__init__.py

pystencils/llvm/control_flow.py

pystencils/llvm/kernelcreation.py

pystencils/llvm/llvm.py

pystencils/llvm/llvmjit.py

pystencils_tests/test_basic_usage_llvm.ipynb

pystencils_tests/test_llvm.py

pystencils_tests/test_size_and_layout_checks_llvm.py

pystencils_tests/test_sliced_iteration.py

pystencils_tests/test_types.py

setup.py