deprecate App.requirements[], was only used for RequiresRoot

RequiresRoot is obsolete as a metadata field since there is the SUPER_USER
permission.  This `requirements` array was set up to handle other things,
but that was never implemented.

app/src/main/java/org/fdroid/fdroid/data/App.java

@@ -113,8 +113,9 @@ public class App extends ValueObject implements Comparable<App>, Parcelable {
     public String[] antiFeatures;
 
     /**
-     * List of special requirements (such as root privileges) or null if there aren't any.
+     * Requires root access (only ever used for root)
      */
+    @Deprecated
     public String[] requirements;
 
     private AppPrefs prefs;