Remove pybind11 submodule

[angela28chen]

No description provided.

[angela28chen]

I have no idea how to test my changes to the jinja file if it's not being tested by the normal host tools build process.

Edit: Useful context: b/430643434. It appears that generateSOAs.py is run manually and infrequently and the process is not documented. I have tried running python generateSOAs.py event_state.json from the dive_core subfolder to test these changes (appears that event_state C++ files not altered)

@shanminchao If you can provide some context on which files need to be generated with this python script (if there are files other than event_state.json) and if pybind11 is still required or not, that would be really helpful

[shanminchao]

As far as I know, pybind11 is not used at all by generateSOAs.py. I manually tested this just now using this PR by modifying one of the descriptions in the event_state.json file, ran the script, and found all the appropriate auto-generated files modified. So as far as I'm concerned, this PR is approved.