Remove DesktopTaskView.isDesktopModeSupported

- Use Flags.eanbleDesktopWindowingMode directly
- Also clean up unnecessary and improper flag usage

Bug: 309008406
Flag: ACONFIG com.android.window.flags.enable_desktop_windowing_mode DEVELOPMENT
Test: presubmit
Change-Id: I86ce317ce577f279d2ce819d6dc1738204c2631e
diff --git a/src/com/android/launcher3/Launcher.java b/src/com/android/launcher3/Launcher.java
index 72977ee..020b34e 100644
--- a/src/com/android/launcher3/Launcher.java
+++ b/src/com/android/launcher3/Launcher.java
@@ -2730,7 +2730,7 @@
 
     private void updateDisallowBack() {
         if (Flags.enableDesktopWindowingMode()) {
-            // Do not disable back in launcher when prototype behavior is enabled
+            // TODO(b/330183377) disable back in launcher when when we productionize
             return;
         }
         LauncherRootView rv = getRootView();