[bindings] Remove LLVM python bindings

The LLVM python bindings are defunct.

They have not seen any substantial active development since 2014.

The version number, which is used to find the libLLVM-NN.so library, has
not been updated since LLVM 10.0 (2019) (and even then they were
probably mostly broken)

After fixing the version number to be able to run them at all, a large
number of tests in the test suite fails.

Already in 2017 the removal was discussed:
 https://discourse.llvm.org/t/is-anyone-using-still-using-the-python-bindings/46063
 https://lists.llvm.org/pipermail/llvm-dev/2017-August/116857.html

There exist external projects providing python bindings for LLVM, e.g:
 https://github.com/numba/llvmlite

Differential Revision: https://reviews.llvm.org/D150642