fix: remove 'v12' entry from targets.json

Removed the 'v12' entry from targets.json.

Author: pfeerick

targets.json

@@ -247,11 +247,6 @@
       "description": "FrSky X-Lite S",
       "tags": ["stdlcd"]
     },
-    "v12": {
-      "description": "HelloRadioSky V12",
-      "version_supported": ">= v2.11.0",
-      "tags": ["stdlcd"]
-    },
     "v14": {
       "description": "HelloRadioSky V14",
       "version_supported": ">= v2.11.0",