Remove detachChildren

Since there are no longer callers of detachChildren, remove code and
test that involve detachChildren

Test: Builds and remaining tests pass
Bug: 177557720
Change-Id: Id5b7120b7f2c289d4e7ffb5565b29e2be18d6587
diff --git a/services/surfaceflinger/BufferStateLayer.cpp b/services/surfaceflinger/BufferStateLayer.cpp
index 0cc15c2..3dc62e3 100644
--- a/services/surfaceflinger/BufferStateLayer.cpp
+++ b/services/surfaceflinger/BufferStateLayer.cpp
@@ -216,8 +216,7 @@
     // Returns true if the most recent Transaction applied to CurrentState will be presented.
     return (getSidebandStreamChanged() || getAutoRefresh() ||
             (mCurrentState.modified &&
-             (mCurrentState.buffer != nullptr || mCurrentState.bgColorLayer != nullptr))) &&
-        !mLayerDetached;
+             (mCurrentState.buffer != nullptr || mCurrentState.bgColorLayer != nullptr)));
 }
 
 /* TODO: vhau uncomment once deferred transaction migration complete in
@@ -461,11 +460,6 @@
     return willPresent;
 }
 
-void BufferStateLayer::forceSendCallbacks() {
-    mFlinger->getTransactionCompletedThread().finalizePendingCallbackHandles(
-            mCurrentState.callbackHandles, std::vector<JankData>());
-}
-
 bool BufferStateLayer::setTransparentRegionHint(const Region& transparent) {
     mCurrentState.transparentRegionHint = transparent;
     mCurrentState.modified = true;