Revert "BUG/MEDIUM: connections: force connections cleanup on server changes"

Revert "BUG/MEDIUM: connections: force connections cleanup on server changes"

As explained by Christopher on github issue #665:
In 2.2, srv->idle_conns and srv->safe_conns are thread-safe lists. But
not in 2.1. So the patch must be reverted or the lists must be changed
to use mt_list instead. The same must be done in 2.0, but the mt_list
does not exist on this version.

I choose to revert it as the original bug is truly revealed in v2.2
after commit 079cb9af22da6 ("MEDIUM: connections: Revamp the way idle
connections are killed")

this should resolve github issue #665

this reverts commit 7eab37b6819af685c647cf5a581e29fca2f3e079.
this reverts commit 3ad3306ec0bcb0cd4ca2b9ba134ed67663473ee8.

The patch was directly introduced on 2.1, there is no upstream commit ID for
this patch.