Remove LOCAL_SRC_FILES as precondition of enabling dexpreopt

Because a library or app can be built from mere static libraries,
or generated java files. For example, framework is built from only
static library framework-base but without LOCAL_SRC_FILES.
Also added framework2 to PRODUCT_PACKAGES.
Previously framework2.jar was installed by dependency explicitly
established in frameworks/base/Android.mk. That's not enough for the
.odex file.
This fixed the boot failure reported in bug 12382916.

Bug: 12382916
Change-Id: If1a70261ab2bb7fef77cf7b7b995bdc029be0fc3