Don't keep LayoutlibCallback reference. [DO NOT MERGE]

Switch to the newer API that enables keeping a reference only to the
ParserFactory which is a much leaner object as compared to
LayoutlibCallback.

 Conflicts:
	tools/layoutlib/bridge/tests/src/com/android/layoutlib/bridge/android/BridgeXmlBlockParserTest.java

Change-Id: I9b7afd93226db23786a00b2951cbf5ae5b8f3e5f
(cherry picked from commit f2d408b5)