px4io: moving mixing to FMU side

Using mixers on the IO side had a remote benefit of being able to
override all control surfaces with a radio remote on a fixed wing.
This ended up not being used that much and since the original design
10 years ago (2011) we have been able to convince ourselves that the
overall system stability is at a level where this marginal benefit,
which is not present on multicopters, is not worth the hazzle.

Co-authored-by: Beat Küng <beat-kueng@gmx.net>
Co-authored-by: Daniel Agar <daniel@agar.ca>

src/systemcmds/tests/test_mixer.cpp

@@ -48,7 +48,7 @@
 #include <output_limit/output_limit.h>
 #include <drivers/drv_hrt.h>
 #include <drivers/drv_pwm_output.h>
-#include <px4iofirmware/mixer.h>
+
 #include <px4iofirmware/protocol.h>
 
 #include <uORB/topics/actuator_controls.h>
@@ -277,7 +277,7 @@ bool MixerTest::load_mixer(const char *filename, const char *buf, unsigned loade
 
 	/* reset, load in chunks */
 	mixer_group.reset();
-	char mixer_text[PX4IO_MAX_MIXER_LENGTH];		/* large enough for one mixer */
+	char mixer_text[330];		/* large enough for one mixer */
 
 	unsigned mixer_text_length = 0;
 	unsigned transmitted = 0;
@@ -290,7 +290,7 @@ bool MixerTest::load_mixer(const char *filename, const char *buf, unsigned loade
 		/* check for overflow - this would be really fatal */
 		if ((mixer_text_length + text_length + 1) > sizeof(mixer_text)) {
 			PX4_ERR("Mixer text length overflow for file: %s. Is PX4IO_MAX_MIXER_LENGTH too small? (curr len: %d)", filename,
-				PX4IO_MAX_MIXER_LENGTH);
+				330);
 			return false;
 		}