Remove extraneous comment.

tools/dockerfile/grpc_artifact_protoc/Dockerfile

@@ -51,8 +51,6 @@ RUN bash -c 'echo "enabled=1" >> /etc/yum.repos.d/devtools-1.1.repo'
 RUN bash -c "sed -e 's/\$basearch/i386/g' /etc/yum.repos.d/devtools-1.1.repo > /etc/yum.repos.d/devtools-i386-1.1.repo"
 RUN sed -e 's/testing-/testing-i386-/g' -i /etc/yum.repos.d/devtools-i386-1.1.repo
 
-# Make yum install twice to overcome docker issue when using overlay storage driver.
-
 # We'll get and "Rpmdb checksum is invalid: dCDPT(pkg checksums)" error caused by
 # docker issue when using overlay storage driver, but all the stuff we need
 # will be installed, so for now we just ignore the error.
@@ -62,4 +60,4 @@ RUN yum install -y devtoolset-1.1 \
                    devtoolset-1.1-libstdc++-devel.i686 || true
 
 # Start in devtoolset environment that uses GCC 4.7
-CMD ["scl", "enable", "devtoolset-1.1", "bash"]
+CMD ["scl", "enable", "devtoolset-1.1", "bash"]