Auto env setting does not work anymore since OTB 9

A big part of the helpers module was functions to find and set paths / env for importing otbApplication, without the need to source otbenv.profile.
It allowed import pyotb even if only the python lib as in PATH, or when setting env var OTB_ROOT.

Since packaging changed, it's now required to also set LD_LIBRARY_PATH in order to import without errors. And this cannot be done from a running process, only before launching python.

I haven't checked for windows, but I guess the problem is similar.

So I guess we could remove all of this useless code now, especially if the install process / python env setting is now better handled. I'm probably the only one using OTB_ROOT env var anyway (it was really handy to switch OTB versions).