Unpin the version of python-ldap3 in Dockerfile-tests since a new version has been released

docker/Dockerfile-tests

@@ -4,7 +4,6 @@ WORKDIR /build
 RUN yum -y update
 RUN yum -y install epel-release yum-utils
 RUN yum-config-manager --add-repo https://kojipkgs.fedoraproject.org/repos-dist/epel7Server-infra/latest/x86_64/
-# TODO: Unpin the version of python-ldap3 after 2.6.1 is released
 RUN yum -y install \
     --nogpgcheck \
     --setopt=deltarpm=0 \
@@ -29,7 +28,7 @@ RUN yum -y install \
     python-funcsigs \
     python-futures \
     python-koji \
-    https://kojipkgs.fedoraproject.org//packages/python-ldap3/2.6/1.el7/noarch/python2-ldap3-2.6-1.el7.noarch.rpm \
+    python-ldap3 \
     python-mock \
     python-munch \
     python-pip \