Remove imgin support

Since the current testing suite assumes more than one instance per
service, imgin causes the tests to fail, since there is only one
public instance.

Rather than refactor the tests to accommodate for services with only one
instance, imgin has been removed until there are multiple instances
available.

services.json

@@ -193,14 +193,6 @@
       "https://rimgo.bus-hit.me"
     ]
   },
-  {
-    "type": "imgin",
-    "test_url": "/a/H8M4rcp",
-    "fallback": "https://imgin.voidtech.net",
-    "instances": [
-      "https://imgin.voidnet.tech"
-    ]
-  },
   {
     "type": "whoogle",
     "test_url": "/search?cookies_disabled=1&q=<%=query%>",