MINOR: pools: Don't dump anymore info about pools when purge is forced

MINOR: pools: Don't dump anymore info about pools when purge is forced

Historically, when the purge of pools was forced by sending a SIGQUIT to
haproxy, information about the pools were first dumped. It is now totally
pointless because these info can be retrieved via the CLI. It is even less
relevant now because the purge is forced typically when there are memroy
issues and to dump pools information, data must be allocated.

dump_pools_info() function was simplified because it is now called only from
an applet. No reason to still try to dump info on stderr.