Revert "chg: always delete netmatch .so files when loaded successfully."

This reverts commit a7f9b6ebd825c930939c9ce19dee9a670f43bed0.

Problem is that gdb is very confused by the disapearance of the .so
file ; so, look for another solution (such as mass deletion at exit).
chg: add assertion wrt. ref
Revert "fix: wrong assertion about NOT_IN_DEATH_ROW"

This reverts commit c2ac0e806ae565ce9eb4221fd64b23a7f09f0b30.

Some plugins need this indication :-(
chg: dev: Definitive guide to NOT_IN_DEATH_ROW