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/busctl/busctl-introspect.c

@@ -544,7 +544,6 @@ static int parse_xml_node(Context *context, const char *prefix, unsigned n_depth
 
                         break;
 
-
                 case STATE_SIGNAL_ARG:
 
                         if (t == XML_ATTRIBUTE_NAME) {

src/busctl/busctl.c

@@ -1462,7 +1462,6 @@ static int message_append_cmdline(sd_bus_message *m, const char *signature, char
                         break;
                 }
 
-
                 case SD_BUS_TYPE_DOUBLE: {
                         double z;
 
@@ -1980,7 +1979,6 @@ static int parse_argv(int argc, char *argv[]) {
                         arg_expect_reply = !!r;
                         break;
 
-
                 case ARG_AUTO_START:
                         r = parse_boolean(optarg);
                         if (r < 0) {
@@ -1991,7 +1989,6 @@ static int parse_argv(int argc, char *argv[]) {
                         arg_auto_start = !!r;
                         break;
 
-
                 case ARG_ALLOW_INTERACTIVE_AUTHORIZATION:
                         r = parse_boolean(optarg);
                         if (r < 0) {