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/mautic.json

@@ -15,12 +15,6 @@
       "eoas": "2025-12-31",
       "eol": "2025-12-31"
     },
-    "6.0": {
-      "name": "6.0"
-    },
-    "5.2": {
-      "name": "5.2"
-    },
     "5.1": {
       "name": "5.1",
       "releaseDate": "2024-06-13",
@@ -82,9 +76,6 @@
       "eoas": "2020-11-23",
       "eol": "2020-11-30"
     },
-    "3.0": {
-      "name": "3.0"
-    },
     "2.16": {
       "name": "2.16",
       "releaseDate": "2020-02-13",