LU-6142 lnet: discard lnet_current_net_count

The variable lnet_current_net_count is never used.  So remove it.
The function lnet_get_net_count() is only used to update thar
variable, so remove it too.

Test-Parameters: trivial
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Change-Id: Id61f381f6220356c5b96c8a5822d8748a8ba43a4
Reviewed-on: https://review.whamcloud.com/44089
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>