Update deprecated methods

The `set_state` and `remove_state` methods have been deprecated in
favour of `set_flag` and `clear_flag`. This updates the references to
those methods.
diff --git a/juju-charms/layers/simple/reactive/simple.py b/juju-charms/layers/simple/reactive/simple.py
index 2a55a5c..8355bf3 100644
--- a/juju-charms/layers/simple/reactive/simple.py
+++ b/juju-charms/layers/simple/reactive/simple.py
@@ -5,8 +5,8 @@
     status_set,
 )
 from charms.reactive import (
-    remove_state as remove_flag,
-    set_state as set_flag,
+    clear_flag,
+    set_flag,
     when,
     when_not,
 )
@@ -41,4 +41,4 @@
     else:
         action_set({'outout': result})
     finally:
-        remove_flag('actions.touch')
+        clear_flag('actions.touch')