Update default state for whether legacy passwords are disabled.

This was a feature that was removed from the app over 4.5 years ago.
The value should have been manually set to false when they set a
password, meaning that it should be safe to set the default to true.

Fixes #10367

app/src/main/java/org/thoughtcrime/securesms/util/TextSecurePreferences.java

@@ -649,7 +649,7 @@ public class TextSecurePreferences {
   }
 
   public static boolean isPasswordDisabled(Context context) {
-    return getBooleanPreference(context, DISABLE_PASSPHRASE_PREF, false);
+    return getBooleanPreference(context, DISABLE_PASSPHRASE_PREF, true);
   }
 
   public static void setPasswordDisabled(Context context, boolean disabled) {