Drop commands about Python 3.4 in manylinux2010 Dockerfile

tools/dockerfile/grpc_artifact_python_manylinux2010_x64/Dockerfile

@@ -24,7 +24,6 @@ RUN yum install -y curl-devel expat-devel gettext-devel linux-headers openssl-de
 # Install Python build requirements
 RUN /opt/python/cp27-cp27m/bin/pip install --upgrade cython
 RUN /opt/python/cp27-cp27mu/bin/pip install --upgrade cython
-RUN /opt/python/cp34-cp34m/bin/pip install --upgrade cython
 RUN /opt/python/cp35-cp35m/bin/pip install --upgrade cython
 RUN /opt/python/cp36-cp36m/bin/pip install --upgrade cython
 RUN /opt/python/cp37-cp37m/bin/pip install --upgrade cython

tools/dockerfile/grpc_artifact_python_manylinux2010_x86/Dockerfile

@@ -24,7 +24,6 @@ RUN yum install -y curl-devel expat-devel gettext-devel linux-headers openssl-de
 # Install Python build requirements
 RUN /opt/python/cp27-cp27m/bin/pip install --upgrade cython
 RUN /opt/python/cp27-cp27mu/bin/pip install --upgrade cython
-RUN /opt/python/cp34-cp34m/bin/pip install --upgrade cython
 RUN /opt/python/cp35-cp35m/bin/pip install --upgrade cython
 RUN /opt/python/cp36-cp36m/bin/pip install --upgrade cython
 RUN /opt/python/cp37-cp37m/bin/pip install --upgrade cython