Reset update-flag on uninstall (#2025)

* Reset update-flag on uninstall

If there is an update available when the extension is uninstalled, the
table will still have the update flag, which makes no sense if it is not
installed.

Example:
```
{
  "pkgName": "eu.kanade.tachiyomi.extension.en.comix",
  "name": "Comix",
  "lang": "en",
  "versionCode": 20,
  "versionName": "1.4.20",
  "iconUrl": "/api/v1/extension/icon/tachiyomi-en.comix-v1.4.20.apk",
  "repo": "<hidden>",
  "isNsfw": true,
  "isInstalled": false,
  "isObsolete": false,
  "hasUpdate": true,
  "__typename": "ExtensionType"
},
```

* Update changelog

server/src/main/kotlin/suwayomi/tachidesk/manga/impl/extension/Extension.kt

@@ -358,6 +358,7 @@ object Extension {
                 } else {
                     ExtensionTable.update({ ExtensionTable.pkgName eq pkgName }) {
                         it[isInstalled] = false
+                        it[hasUpdate] = false
                     }
                 }