refactoring: simplify the semaphorewait logic

The semaphorewait()/waitforthread() logic is usefull for IMAP starting
connections. We actually use it in imapserver only.

This patch removes the over-engineered factorized methods. It tend to simplify
the code by cleaning out a chain of two direct calls with no other processes.

Reviewed-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/folder/Base.py

@@ -37,11 +37,6 @@ class BaseFolder(object):
         false otherwise.  Probably only IMAP will return true."""
         return 0
 
-    def waitforthread(self):
-        """For threading folders, waits until there is a resource available
-        before firing off a thread.  For all others, returns immediately."""
-        pass
-
     def getcopyinstancelimit(self):
         """For threading folders, returns the instancelimitname for
         InstanceLimitedThreads."""