Fix: controller: avoid use-after-free when disconnecting proxy IPCs during shutdown

Previously internal_lrm_state_destroy() directly freed and removed any
relevant proxy entries from proxy_table, which could potentially leave
the proxy IPCs connected and cause use-after-free when
g_main_context_dispatch() -> ... -> remote_proxy_disconnected() was
later called in crmd_exit().

The solution is to make sure any connected proxies get disconnected. So
that remote_proxy_disconnected() will be called and as well remove the
entries from proxy_table.