Fix memory leak in HWUI

std::unique_ptr::release just releases the ownership of the
managed object. To delete the object, std::unique_ptr::reset
function should be called.

Change-Id: If65f74085b1fc2be3a9fffc433326e0bcdb40ff3
diff --git a/libs/hwui/Caches.cpp b/libs/hwui/Caches.cpp
index aa73d44..2763e89 100644
--- a/libs/hwui/Caches.cpp
+++ b/libs/hwui/Caches.cpp
@@ -117,7 +117,7 @@
 
 void Caches::terminate() {
     if (!mInitialized) return;
-    mRegionMesh.release();
+    mRegionMesh.reset(nullptr);
 
     fboCache.clear();