Config.in: remove BR2_DEPRECATED_SINCE_2015_05

It's now unused.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

Config.in

@@ -369,10 +369,6 @@ config BR2_DEPRECATED
 
 if BR2_DEPRECATED
 
-config BR2_DEPRECATED_SINCE_2015_05
-	bool
-	default y
-
 config BR2_DEPRECATED_SINCE_2015_08
 	bool
 	default y