Removing mentioned stable support for Debian 9
Removing mentioned stable support for Debian 9

As there is no file `INSTALL.debian9.txt` and we only have a file with the name `xINSTALL.debian9.txt`. The Debian 9 support seems to be experimental.
MISP/MISP,SteveClement/MISP,MISP/MISP,MISP/MISP,MISP/MISP,SteveClement/MISP,SteveClement/MISP,SteveClement/MISP,MISP/MISP,SteveClement/MISP