Revert "Flip BLAST flag."

This reverts commit 5cf36637f9.

Reason for revert: b/171938419

Change-Id: I81dd1c3482c6fcbc527ec737d158b9d9a23fcbbe

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

@@ -1203,7 +1203,9 @@ public class WindowManagerService extends IWindowManager.Stub
         mAnimator = new WindowAnimator(this);
         mRoot = new RootWindowContainer(this);
 
-        mUseBLAST = true;
+        mUseBLAST = DeviceConfig.getBoolean(
+                    DeviceConfig.NAMESPACE_WINDOW_MANAGER_NATIVE_BOOT,
+                    WM_USE_BLAST_ADAPTER_FLAG, false);
 
         mSyncEngine = new BLASTSyncEngine(this);