tree-wide: drop spurious newlines (#8764)

Double newlines (i.e. one empty lines) are great to structure code. But
let's avoid triple newlines (i.e. two empty lines), quadruple newlines,
quintuple newlines, …, that's just spurious whitespace.

It's an easy way to drop 121 lines of code, and keeps the coding style
of our sources a bit tigther.

src/network/netdev/dummy.c

@@ -6,7 +6,6 @@
   Copyright 2014 Tom Gundersen
 ***/
 
-
 #include "netdev/dummy.h"
 
 const NetDevVTable dummy_vtable = {

src/network/netdev/geneve.c

@@ -150,7 +150,6 @@ static int netdev_geneve_create(NetDev *netdev) {
 
         log_netdev_debug(netdev, "Creating");
 
-
         return r;
 }
 

src/network/netdev/wireguard.c

@@ -315,7 +315,6 @@ static void resolve_endpoints(NetDev *netdev) {
         }
 }
 
-
 static int netdev_wireguard_post_create(NetDev *netdev, Link *link, sd_netlink_message *m) {
         Wireguard *w;
 
@@ -455,7 +454,6 @@ int config_parse_wireguard_preshared_key(const char *unit,
                                    peer->preshared_key);
 }
 
-
 int config_parse_wireguard_public_key(const char *unit,
                                       const char *filename,
                                       unsigned line,