Since all regrtest -j output is now done in the main thread we are no
longer using the print lock, so remove it.
diff --git a/Lib/test/regrtest.py b/Lib/test/regrtest.py
index 060fb83..52f5cfd 100755
--- a/Lib/test/regrtest.py
+++ b/Lib/test/regrtest.py
@@ -440,13 +440,12 @@
                 resource_denieds.append(test)
 
     if use_mp:
-        from threading import Thread, Lock
+        from threading import Thread
         from queue import Queue, Empty
         from subprocess import Popen, PIPE, STDOUT
         from collections import deque
         # TextIOWrapper is not entirely thread-safe now,
         # it can produce duplicate output when printing from several threads.
-        print_lock = Lock()
         debug_output_pat = re.compile(r"\[\d+ refs\]$")
         pending = deque()
         output = Queue()