Fixes for posix-arm and qurt builds

Ifdefed out deadcode in position_estimator_inav_main.c as the
deadcode does not compile for qurt.

Added fixes to get a successful build for posix-arm and qurt targets.
Removed CLOCK_REALTIME def from px4_time.h for qurt and removed unused
variables in att_est_q and mc_att_control.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/modules/attitude_estimator_q/attitude_estimator_q_main.cpp

@@ -47,7 +47,6 @@
 #include <poll.h>
 #include <fcntl.h>
 #include <float.h>
-#include <termios.h>
 #include <errno.h>
 #include <limits.h>
 #include <math.h>