getMemoryClass -> getLargeMemoryClass

Fixes #6812

// FREEBIe

src/org/thoughtcrime/securesms/util/Util.java

@@ -428,7 +428,7 @@ public class Util {
     ActivityManager activityManager = (ActivityManager) context.getSystemService(Context.ACTIVITY_SERVICE);
 
     return (VERSION.SDK_INT >= VERSION_CODES.KITKAT && activityManager.isLowRamDevice()) ||
-           activityManager.getMemoryClass() <= 64;
+           activityManager.getLargeMemoryClass() <= 64;
   }
 
   public static int clamp(int value, int min, int max) {