[ci] Stop symlinking python36 to python3 on CentOS

CentOS recently started to provide python3 by default obsoleted python36. Our
manual hack broke the test suite and is no longer required.

(cherry picked from commit e22c97e1cee806b9e7ecf7a06c31dab959c6c31c)

ci/install_dependencies.sh

@@ -49,14 +49,8 @@ case "$distro_id" in
         # enable copr for gtest
         curl https://copr.fedorainfracloud.org/coprs/defolos/devel/repo/epel-7/defolos-devel-epel-7.repo > /etc/yum.repos.d/_copr_defolos-devel.repo
         yum clean all
-        yum -y install gcc-c++ clang cmake3 make ccache expat-devel zlib-devel libssh-devel libcurl-devel gtest-devel which python36 dos2unix
-        # symlink up to date versions of python & cmake to 'default' names
-        if [ ! -e /usr/bin/python3 ]; then
-            ln -s /usr/bin/python36 /usr/bin/python3
-        elif [ -L /usr/bin/python3 ]; then
-            rm /usr/bin/python3
-            ln -s /usr/bin/python36 /usr/bin/python3
-        fi
+        yum -y install gcc-c++ clang cmake3 make ccache expat-devel zlib-devel libssh-devel libcurl-devel gtest-devel which python3 dos2unix
+        # symlink up to date versions of cmake to 'default' name
         mv /bin/cmake /bin/.cmake.old
         ln -s /bin/cmake3 /bin/cmake
         ;;