Land #2413, axe callcc

This is the only time callcc is used in the entire codebase, too, so
this apparently removes a roadblack to non-MRI Rubies, so that's nice.

lib/rex/sync/event.rb

@@ -61,22 +61,12 @@ class Event
   # Waits for the event to become signaled.  Timeout is measured in
   # seconds.  Raises TimeoutError if the condition does not become signaled.
   #
-
-  begin
-    # XXX: we need to replace this code
-    #      continuations slow down YARV
-    require "continuation" if not defined? callcc
-  rescue ::LoadError
-  end
-
   def wait(t = Infinite)
-    callcc { |ctx|
-      self.mutex.synchronize {
-        ctx.call if (self.state == true)
+    self.mutex.synchronize {
+      break if (self.state == true)
 
-        Timeout.timeout(t) {
-          self.cond.wait(self.mutex)
-        }
+      Timeout.timeout(t) {
+        self.cond.wait(self.mutex)
       }
     }