Don't rely on python3-ldap

tox.ini

@@ -21,16 +21,10 @@ deps =
   {[base]deps}
 
 [testenv:py31]
-deps =
-  python3-ldap
-  {[base]deps}
+deps = {[base]deps}
 
 [testenv:py32]
-deps =
-  python3-ldap
-  {[base]deps}
+deps = {[base]deps}
 
 [testenv:py33]
-deps =
-  python3-ldap
-  {[base]deps}
+deps = {[base]deps}