MEDIUM: server: Don't introduce a new server-state file version

MEDIUM: server: Don't introduce a new server-state file version

This revert the commit 63e6cba12 ("MEDIUM: server: add server-states version
2"), but keeping all recent features added to the server-sate file. Instead
of adding a 2nd version for the server-state file format to handle the 5 new
fields added during the 2.4 development, these fields are considered as
optionnal during the parsing. So it is possible to load a server-state file
from HAProxy 2.3. However, from 2.4, these new fields are always dumped in
the server-state file. But it should not be a problem to load it on the 2.3.

This patch seems a bit huge but the diff ignoring the space is much smaller.

The version 2 of the server-state file format is reserved for a real
refactoring to address all issues of the current format.