Move event-que declarations to sysdeps, new backend interface process_removed

- the reason being that the que-handling was declared on global level, but
  was only implemented in one back end.  If this is deemed generally useful,
  it should all be moved to front end, but as things are it's all the same,
  so I'm preferring the less invasive change
diff --git a/sysdeps/linux-gnu/proc.c b/sysdeps/linux-gnu/proc.c
index c5282e4..97969dc 100644
--- a/sysdeps/linux-gnu/proc.c
+++ b/sysdeps/linux-gnu/proc.c
@@ -15,10 +15,12 @@
 #include <string.h>
 #include <unistd.h>
 
+#include "config.h"
 #include "common.h"
 #include "breakpoint.h"
 #include "proc.h"
 #include "library.h"
+#include "events.h"
 
 /* /proc/pid doesn't exist just after the fork, and sometimes `ltrace'
  * couldn't open it to find the executable.  So it may be necessary to
@@ -588,3 +590,9 @@
         ret = syscall (__NR_tkill, pid, sig);
 	return ret;
 }
+
+void
+process_removed(struct Process *proc)
+{
+	delete_events_for(proc);
+}