rtapi/rt-preempt: remove dead code, clarify RTAPI/ULAPI
rtapi/rt-preempt: remove dead code, clarify RTAPI/ULAPI

all threads-related defs, data and code is RTAPI only.

The rtapi_init/rtapi_exit array handling code for RTAPI is useless (it
is not present in xenomai either since the modules are managed in rtapi_app as
DSO's and need no representation at the RTAPI level for user threads).

As a bonus, ID assignment is now consistent across flavors as all ID's
are assigned through rtapi_next_handle().


This patch part of the Haberler "Summer of Less Code" project ;)
Also in the pipe: src/hal/lib -2500 lines.

Cid427/machinekit,Cid427/machinekit,strahlex/machinekit,bobvanderlinden/machinekit,ArcEye/MK-Qt5,unseenlaser/machinekit,kinsamanka/machinekit,RunningLight/machinekit,Cid427/machinekit,mhaberler/machinekit,kinsamanka/machinekit,ArcEye/MK-Qt5,ArcEye/MK-Qt5,mhaberler/machinekit,strahlex/machinekit,ArcEye/machinekit-testing,RunningLight/machinekit,ArcEye/machinekit-testing,unseenlaser/machinekit,araisrobo/machinekit,ArcEye/MK-Qt5,bobvanderlinden/machinekit,strahlex/machinekit,araisrobo/machinekit,kinsamanka/machinekit,RunningLight/machinekit,araisrobo/machinekit,unseenlaser/machinekit,RunningLight/machinekit,unseenlaser/machinekit,mhaberler/machinekit,araisrobo/machinekit,mhaberler/machinekit,unseenlaser/machinekit,RunningLight/machinekit,RunningLight/machinekit,ArcEye/machinekit-testing,bobvanderlinden/machinekit,mhaberler/machinekit,bobvanderlinden/machinekit,kinsamanka/machinekit,ArcEye/MK-Qt5,Cid427/machinekit,mhaberler/machinekit,unseenlaser/machinekit,ArcEye/machinekit-testing,araisrobo/machinekit,strahlex/machinekit,bobvanderlinden/machinekit,bobvanderlinden/machinekit,araisrobo/machinekit,Cid427/machinekit,kinsamanka/machinekit,araisrobo/machinekit,mhaberler/machinekit,bobvanderlinden/machinekit,Cid427/machinekit,araisrobo/machinekit,ArcEye/MK-Qt5,ArcEye/MK-Qt5,strahlex/machinekit,ArcEye/MK-Qt5,Cid427/machinekit,unseenlaser/machinekit,mhaberler/machinekit,ArcEye/machinekit-testing,kinsamanka/machinekit,RunningLight/machinekit,strahlex/machinekit,kinsamanka/machinekit,araisrobo/machinekit,Cid427/machinekit,ArcEye/machinekit-testing,strahlex/machinekit,ArcEye/machinekit-testing,ArcEye/machinekit-testing,bobvanderlinden/machinekit,unseenlaser/machinekit,RunningLight/machinekit,kinsamanka/machinekit