server: fix: remove kept_alive() from server loop

server: fix: remove kept_alive() from server loop

The kept_alive() action is specific of a server that enjoyed an
unscheduled keep_alive and want to communicate it to the keep
alive logic to reschedule next keep_alive().
In server loop we are not expected to call kept_alive().
Remove it!

This call was erroneously added in commit 94e75e0c06c4.
Later, commit 7442b26d45dc properly added the same call in
gdb_put_packet(), but incorrectly left the older in place.

Change-Id: If476410f870eebfbdaccdb1366ba2e9254e2fdf6
Signed-off-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-on: https://review.openocd.org/c/openocd/+/6836
Reviewed-by: Tomas Vanek <vanekt@fbl.cz>
Tested-by: jenkins