Drop support for Oracle Linux

Installing the required  packages fails on Oracle Linux 7. EPEL is
needed but even when adding EPEL the installation of the
nagios-plugins-all package fails due to broken dependencies,
specifically the perl-utf8-all package.

This also happens with Oracle Linux 8 and 9, so it's not clear
whether this module will be able to support Oracle Linux going
forward.

metadata.json

@@ -36,12 +36,6 @@
         "7"
       ]
     },
-    {
-      "operatingsystem": "OracleLinux",
-      "operatingsystemrelease": [
-        "7"
-      ]
-    },
     {
       "operatingsystem": "Scientific",
       "operatingsystemrelease": [