remove 'maxage' argument for read_* methods

'maxage' is not really used at any place. remove it, as this makes
the code cleaner

Change-Id: I6f10b4ab91fc57640336db1832716ca9012eb241
Reviewed-on: https://forge.frm2.tum.de/review/20347
Tested-by: JenkinsCodeReview <bjoern_pedersen@frm2.tum.de>
Reviewed-by: Enrico Faulhaber <enrico.faulhaber@frm2.tum.de>
Reviewed-by: Markus Zolliker <markus.zolliker@psi.ch>

secop_demo/test.py

@@ -44,7 +44,7 @@ class LN2(Readable):
     but the implementation may do anything
     """
 
-    def read_value(self, maxage=0):
+    def read_value(self):
         return round(100 * random.random(), 1)
 
 
@@ -60,7 +60,7 @@ class Heater(Drivable):
                                 ),
     }
 
-    def read_value(self, maxage=0):
+    def read_value(self):
         return round(100 * random.random(), 1)
 
     def write_target(self, target):
@@ -90,7 +90,7 @@ class Temp(Drivable):
         ),
     }
 
-    def read_value(self, maxage=0):
+    def read_value(self):
         return round(100 * random.random(), 1)
 
     def write_target(self, target):