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/react-native.json

@@ -1,69 +1,5 @@
 {
-  "releases": {
-    "0.80": {
-      "name": "0.80"
-    },
-    "0.79": {
-      "name": "0.79"
-    },
-    "0.78": {
-      "name": "0.78"
-    },
-    "0.77": {
-      "name": "0.77"
-    },
-    "0.76": {
-      "name": "0.76"
-    },
-    "0.75": {
-      "name": "0.75"
-    },
-    "0.74": {
-      "name": "0.74"
-    },
-    "0.73": {
-      "name": "0.73"
-    },
-    "0.72": {
-      "name": "0.72"
-    },
-    "0.71": {
-      "name": "0.71"
-    },
-    "0.70": {
-      "name": "0.70"
-    },
-    "0.69": {
-      "name": "0.69"
-    },
-    "0.68": {
-      "name": "0.68"
-    },
-    "0.67": {
-      "name": "0.67"
-    },
-    "0.66": {
-      "name": "0.66"
-    },
-    "0.65": {
-      "name": "0.65"
-    },
-    "0.64": {
-      "name": "0.64"
-    },
-    "0.63": {
-      "name": "0.63"
-    },
-    "0.62": {
-      "name": "0.62"
-    },
-    "0.61": {
-      "name": "0.61"
-    },
-    "0.60": {
-      "name": "0.60"
-    }
-  },
+  "releases": {},
   "versions": {
     "0.78.3": {
       "name": "0.78.3",