NO_JIRA: Remove unneeded python 'global' tripping up flake8 linter

python/proton/_tracing.py

diff --git a/python/proton/_tracing.py b/python/proton/_tracing.py
index d45fd31..72d786d 100644
--- a/python/proton/_tracing.py
+++ b/python/proton/_tracing.py
@@ -42,7 +42,6 @@
 
 
 def get_tracer():
-    global _tracer
     if _tracer is not None:
         return _tracer
     exe = sys.argv[0] if sys.argv[0] else 'interactive-session'