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/eclipse-temurin.json

@@ -4,35 +4,14 @@
       "name": "8",
       "eol": "2026-11-30"
     },
-    "24": {
-      "name": "24"
-    },
-    "23": {
-      "name": "23"
-    },
-    "22": {
-      "name": "22"
-    },
     "21": {
       "name": "21",
       "eol": "2029-12-31"
     },
-    "20": {
-      "name": "20"
-    },
-    "19": {
-      "name": "19"
-    },
-    "18": {
-      "name": "18"
-    },
     "17": {
       "name": "17",
       "eol": "2027-10-31"
     },
-    "16": {
-      "name": "16"
-    },
     "11": {
       "name": "11",
       "eol": "2027-10-31"