Fix output of param show -q XXX on NuttX shell

[MaEtUgR]

Solved Problem

When using e.g. param show -q SYS_AUTOSTART on the NuttX shell I found that it actually doesn't output anything. After looking into the code it prints the same way as other params show variants but without any newline.

Solution

1. Adding a newline makes it work. So the assumption was that without a newline there's no flush to the output console until the task ends. @dagar confirmed that when we talked today and we tried to add fflush(stdout); instead of a newline which also works. But adding the newline should be ok since the standard says trailing newlines get stripped from shell substitutions so we stick with the newline.
2. While at it @dagar suggested removing the legacy PARAM_PRINT defines.

Changelog Entry

Fix output of param show -q XXX on NuttX shell

Test coverage

I tested on fmu-v5x and the parameters show on the MAVLink shell.

SITL SIH still loads, the startup script uses the substitution:

PX4-Autopilot/ROMFS/px4fmu_common/init.d-posix/rcS

Line 209 in da88278

for f in ${R}etc/init.d-posix/airframes/"$(param show -q SYS_AUTOSTART)"_*