tests: use i3_config arg instead of precisely one launch_with_config

This way, tests are shorter, and i3test’s invocation of launch_with_config
parallelizes work better, using dont_block => 1.

testcases/t/263-config-reload-reverts-bind-mode.t

@@ -18,9 +18,7 @@
 # binding mode.
 # Ticket: #2228
 # Bug still in: 4.11-262-geb631ce
-use i3test i3_autostart => 0;
-
-my $config = <<EOT;
+use i3test i3_config => <<EOT;
 # i3 config file (v4)
 font -misc-fixed-medium-r-normal--13-120-75-75-C-70-iso10646-1
 
@@ -28,8 +26,6 @@ mode "othermode" {
 }
 EOT
 
-my $pid = launch_with_config($config);
-
 cmd 'mode othermode';
 
 my $i3 = i3(get_socket_path(0));
@@ -51,6 +47,4 @@ $t = AnyEvent->timer(after => 0.5, cb => sub { $cv->send(0); });
 
 ok($cv->recv, 'Mode event received');
 
-exit_gracefully($pid);
-
 done_testing;