AP_Scripting: refresh serial bindings

[tpwrules]

Removes some annoyances with unnecessary uint32_t_ud and pitfalls with -1 return values. This does technically break compatibility, not sure if there is any policy on that. I tried to edit the scripts in the repo to fix them but user scripts will need to be adjusted in minor ways.

Tested in SITL and on Cube Orange with my REPL script.