Sync against taskchampion-sync-server (#3118)

This removes use of gnutls and the TLS implementation, which is no
longer needed (task synchronization is handled via Taskchampion, which
uses `reqwest`, which handles TLS via other Rust dependencies). This
incidentally removes the following config options:
 * `debug.tls`
 * `taskd.ca`
 * `taskd.certificate`
 * `taskd.ciphers`
 * `taskd.credentials`
 * `taskd.key`
 * `taskd.server`
 * `taskd.trust`

test/basetest/testing.py

@@ -2,8 +2,7 @@
 
 import unittest
 import sys
-from .utils import TASKW_SKIP, TASKD_SKIP
-from .taskd import Taskd
+from .utils import TASKW_SKIP
 
 
 class BaseTestCase(unittest.TestCase):
@@ -21,13 +20,4 @@ class TestCase(BaseTestCase):
     pass
 
 
-@unittest.skipIf(TASKD_SKIP, "TASKD_SKIP set, skipping taskd tests.")
-@unittest.skipIf(Taskd.not_available(), "Taskd binary not available at '{0}'"
-                                        .format(Taskd.DEFAULT_TASKD))
-class ServerTestCase(BaseTestCase):
-    """Automatically skips tests if TASKD_SKIP is present in the environment
-    """
-    pass
-
-
 # vim: ai sts=4 et sw=4