Ardupilot: Copter-4.0 PRs delayed until early June

[rmackay9]

These PRs have been delayed until early April so we can complete stabilizing Copter-4.0 (issues) before making significant structural changes.

• [ ] Copter: refactoring about control_mode https://github.com/ArduPilot/ardupilot/pull/13431
• [ ] Copter: Summarize processes separated by the preprocessor https://github.com/ArduPilot/ardupilot/pull/13806
• [ ] AP_Math: judge isnan judgment before operation https://github.com/ArduPilot/ardupilot/pull/13807
• [ ] Libraries/Copter: Set the gravitational acceleration value to the defined value: https://github.com/ArduPilot/ardupilot/pull/13813
• [x] AP_Baro: Delete unnecessary return processing: https://github.com/ArduPilot/ardupilot/pull/13856
• [x] AP_Avoidance: Change division to multiplication and summarize processing. https://github.com/ArduPilot/ardupilot/pull/13891

[peterbarker]

Remove unnecessary returns - https://github.com/ArduPilot/ardupilot/pull/13856

[peterbarker]

multiplication rather than division in AP_Avoidance: https://github.com/ArduPilot/ardupilot/pull/13891

[amilcarlucas]

I vote to delay these a bit longer. The stable branch needs more time.

[rmackay9]

@amilcarlucas, thanks, I've changed the title a bit..