Remove invalid releases automatically (#466)

Automatically remove empty releases or releases which are released in the future, regardless of the product.

Also refactored a bit releasedata.py to use better names and clarify types.

releases/oracle-database.json

@@ -1,14 +1,5 @@
 {
   "releases": {
-    "9.2": {
-      "name": "9.2"
-    },
-    "9.0": {
-      "name": "9.0"
-    },
-    "23": {
-      "name": "23"
-    },
     "21": {
       "name": "21",
       "eol": "2027-07-31"
@@ -20,24 +11,6 @@
     "18": {
       "name": "18",
       "eol": "2021-06-30"
-    },
-    "12.2": {
-      "name": "12.2"
-    },
-    "12.1": {
-      "name": "12.1"
-    },
-    "11.2": {
-      "name": "11.2"
-    },
-    "11.1": {
-      "name": "11.1"
-    },
-    "10.2": {
-      "name": "10.2"
-    },
-    "10.1": {
-      "name": "10.1"
     }
   },
   "versions": {}