[w3c] Remove redundant RUN command (#6312)

Author: martincostello

test/OpenTelemetry.Instrumentation.W3cTraceContext.Tests/Dockerfile

@@ -31,7 +31,5 @@ RUN apt-get update \
   && cd /usr/local/bin \
   && ln -s /usr/bin/python3 python
 
-# net6.0 image uses Python 3.9, which doesn't have `--break-system-packages` option.
-RUN pip3 install --upgrade pip --break-system-packages || pip3 install --upgrade pip
 RUN pip3 install aiohttp --break-system-packages
 ENTRYPOINT ["dotnet", "vstest", "OpenTelemetry.Instrumentation.W3cTraceContext.Tests.dll", "--logger:console;verbosity=detailed"]