move systemlib/pwm_limit to standalone lib

src/systemcmds/tests/CMakeLists.txt

@@ -93,4 +93,5 @@ px4_add_module(
 		modules__mc_pos_control__mc_pos_control_tests
 		git_ecl
 		ecl_geo_lookup # TODO: move this
+		pwm_limit
 	)

src/systemcmds/tests/test_mixer.cpp

@@ -42,8 +42,8 @@
 #include <string.h>
 
 #include <px4_config.h>
-#include <lib/mixer/mixer.h>
-#include <systemlib/pwm_limit/pwm_limit.h>
+#include <mixer/mixer.h>
+#include <pwm_limit/pwm_limit.h>
 #include <drivers/drv_hrt.h>
 #include <drivers/drv_pwm_output.h>
 #include <px4iofirmware/mixer.h>