Addons with migrated GPIO do not correctly update Pin Mapping

[mikepparks]

It seems that with the new Pin Mapping functionality to allow multiple actions per pin, GPIO migration does not properly occur from previous versions.

To repro, assume an upgrade to #1216 and attempt the following.

• Start with release 0.7.10
• Enable the Tilt addon, and set Tilt 1 to a free GPIO pin. All other values can remain at their defaults.
• Save & Restart
• Update to build Standalone Directional Input actions and Addon buttons as GpioAction #1216

Expectation:
A GpioAction::ANALOG_DIRECTION_MOD_LOW definition should be assigned in Pin Mapping to the Pin previously defined in Tilt 1.

Issue:
The Pin in Pin Mapping remains GpioAction::ASSIGNED_TO_ADDON and cannot be unassigned. The previous value in the addon itself is not updated in the proto data.