doc/adapter-api: Fix SetDiscoveryFilter documentation

The method is not set as experimental for while.
diff --git a/doc/adapter-api.txt b/doc/adapter-api.txt
index 97462a3..08de6cd 100644
--- a/doc/adapter-api.txt
+++ b/doc/adapter-api.txt
@@ -45,7 +45,7 @@
 			Possible errors: org.bluez.Error.InvalidArguments
 					 org.bluez.Error.Failed
 
-		void SetDiscoveryFilter(dict filter) [Experimental]
+		void SetDiscoveryFilter(dict filter)
 
 			This method sets the device discovery filter for the
 			caller. When this method is called with no filter