Remove the SOCD mode addon, fold it into core

[bsstephan]

Same idea as #941, we have some tech debt in the SOCD slider being half in an addon, half in core, and that is confusing to people because they map the pins in the Pin Mapping page and think they're done, without realizing they need to enable the addon, and on the flip side the addon doesn't really do anything all that special other than manage a setting.

#941 set the precedent of having an "active" DP mode, and the same idea would apply here; basically rinse and repeat:

1. Create an activeSOCDCleanerMode in the core gamepad
2. Move the mapping of the pins from the addon to core
3. Have the active mode default to whatever is in the gamepad config, unless one of the mapped pins for the other modes is active
4. Use the active mode in the core gamepad checks, rather than what is in the config
5. Remove the addon from the firmware and webconfig
6. Point DDI and Display code (and maybe more?) at getActiveSOCDCleanerMode()