[lldb/swig] Remove deprecated flags for generating bindings

This patch conditionaly removes the `-py3` swig flag that was used to
generate python3 bindings, since it's unsued since SWIG 4.1.0.

```
Deprecated command line option: -py3. Ignored, this option is no longer supported
```

This also removes the `-shadow` flag that have been deprecated since 2002.

Differential Revision: https://reviews.llvm.org/D142245



Signed-off-by: Med Ismail Bennani <medismail.bennani@gmail.com>