[lldb] Part 2 of 2 - Refactor `CommandObject::DoExecute(...)` return `void` (not `bool`) (#69991)

[lldb] Part 2 of 2 - Refactor `CommandObject::DoExecute(...)` to return
`void` instead of ~~`bool`~~

Justifications:
- The code doesn't ultimately apply the `true`/`false` return values.
- The methods already pass around a `CommandReturnObject`, typically
with a `result` parameter.
- Each command return object already contains:
	- A more precise status
	- The error code(s) that apply to that status

Part 1 refactors the `CommandObject::Execute(...)` method.
- See
[https://github.com/llvm/llvm-project/pull/69989](https://github.com/llvm/llvm-project/pull/69989)

rdar://117378957