remove empty default munge key (nonfunctional change, just clearer)

Author: sjpb

defaults/main.yml

@@ -48,7 +48,7 @@ ohpc_release_repos:
   "7": "https://github.com/openhpc/ohpc/releases/download/v1.3.GA/ohpc-release-1.3-1.el7.x86_64.rpm" # ohpc v1.3 for Centos 7
   "8": "http://repos.openhpc.community/OpenHPC/2/CentOS_8/x86_64/ohpc-release-2-1.el8.x86_64.rpm" # ohpc v2 for Centos 8
 openhpc_slurm_configless: false
-openhpc_munge_key: ''
+openhpc_munge_key:
 openhpc_login_only_nodes: ''
 openhpc_module_system_install: true