Fix some glib deprecation warnings

Most of these have been deprecated since forever (2.2), but they didn't
raise warnings. Now they do, and the warnings are not the most verbose
warnings you could ask for, but, they point in the right direction.

This doesn't handle the GTimeVal deprecation warnings. Those seem
trickier since they cover API, will look into those right after this.

fuzz-support/fuzz.diff

@@ -150,7 +150,7 @@ index ad79e0c..84d0c5c 100644
 +++ b/src/fe-text/irssi.c
 @@ -314,20 +314,16 @@ int main(int argc, char **argv)
  	textui_finish_init();
- 	main_loop = g_main_new(TRUE);
+ 	main_loop = g_main_loop_new(NULL, TRUE);
  
 +#ifdef __AFL_HAVE_MANUAL_CONTROL
 +	__AFL_INIT();
@@ -162,7 +162,7 @@ index ad79e0c..84d0c5c 100644
  	   can call our dirty-checker after each iteration */
  	while (!quitting) {
 -		term_refresh_freeze();
- 		g_main_iteration(TRUE);
+ 		g_main_context_iteration(NULL, TRUE);
 -                term_refresh_thaw();
 -
 -		if (reload_config) {
@@ -174,7 +174,7 @@ index ad79e0c..84d0c5c 100644
 -		dirty_check();
  	}
  
- 	g_main_destroy(main_loop);
+ 	g_main_loop_unref(main_loop);
 diff --git a/src/fe-text/term-terminfo.c b/src/fe-text/term-terminfo.c
 index b2478c6..cebe260 100644
 --- a/src/fe-text/term-terminfo.c