Revert "Query to SystemProperties for BLAST Flag"

This reverts commit 21bb59188e.

Reason for revert: No permissions to read flag value due to sepolicy.

Change-Id: I7043f7abf7025be622d90a4e720b5deafe315ce8

services/core/java/com/android/server/wm/WindowManagerService.java

@@ -1169,10 +1169,9 @@ public class WindowManagerService extends IWindowManager.Stub
         mAnimator = new WindowAnimator(this);
         mRoot = new RootWindowContainer(this);
 
-        mUseBLAST = SystemProperties.getBoolean(
-                    String.join(".", "persist.device_config",
+        mUseBLAST = DeviceConfig.getBoolean(
                     DeviceConfig.NAMESPACE_WINDOW_MANAGER_NATIVE_BOOT,
-                    WM_USE_BLAST_ADAPTER_FLAG), false);
+                    WM_USE_BLAST_ADAPTER_FLAG, false);
 
         mWindowPlacerLocked = new WindowSurfacePlacer(this);
         mTaskSnapshotController = new TaskSnapshotController(this);