This is the only user of nosystem, and it doesn't seem to serve
any purpose since most of the system flags are then manually
included back again. Switch to optimization + obfuscation and
let the build system provide the correct flags file.
Test: classes.dex is identical, classes-proguard.jar differs only
in removed StackMapTable sections (from -dontpreverify?).
Change-Id: I6bae85d10311a982d68cc296a441196ee3115c3d
Colin Cross