minor clean-up: remove duplicate dyn_file_func setting

`self.dyn_file_func` is currently set twice: Once in the base class and once in
the server child class.  As it's only used in the non-server case, remove it
from the base class.

tftpy/TftpContexts.py

@@ -67,7 +67,7 @@ class TftpMetrics(object):
 class TftpContext(object):
     """The base class of the contexts."""
 
-    def __init__(self, host, port, timeout, dyn_file_func=None):
+    def __init__(self, host, port, timeout):
         """Constructor for the base context, setting shared instance
         variables."""
         self.file_to_transfer = None
@@ -94,7 +94,6 @@ class TftpContext(object):
         self.last_update = 0
         # The last packet we sent, if applicable, to make resending easy.
         self.last_pkt = None
-        self.dyn_file_func = dyn_file_func
         # Count the number of retry attempts.
         self.retry_count = 0
 
@@ -199,11 +198,11 @@ class TftpContextServer(TftpContext):
                              host,
                              port,
                              timeout,
-                             dyn_file_func
                              )
         # At this point we have no idea if this is a download or an upload. We
         # need to let the start state determine that.
         self.state = TftpStateServerStart(self)
+
         self.root = root
         self.dyn_file_func = dyn_file_func