FW attitude control scaling fixes and cleanup (#15256)

* FW attitude control scaling fixes and cleanup

This commit aligns the scaling better with the derivations in
https://dev.px4.io/master/en/flight_stack/controller_diagrams.html#airspeed-scaling

Integrator terms now scale with IAS^2 (all three axes)

To match the roll and pitch controllers:
- Yaw integrator scale is now applied during accumulation, not to
  integral value (so now FW_YR_IMAX is respected more intuitively)
- Yaw FF term now scale with IAS instead of IAS^2

Also made a number of small changes to make the three files
  (roll, pitch, yaw) 3-way diffable to be clearer about what the
  differences among them are.

* Remove unused yaw coordination method

- "Coordination method" open vs. closed code removed, since closed
  is never used and not actually implemented.
- No change to behavior

* Remove PX4_WARN messages

Co-authored-by: george <george@campsix.com>

src/modules/fw_att_control/ecl_roll_controller.h

@@ -1,6 +1,6 @@
 /****************************************************************************
  *
- *   Copyright (c) 2013 Estimation and Control Library (ECL). All rights reserved.
+ *   Copyright (c) 2013-2020 Estimation and Control Library (ECL). All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions