Fix desugaring when LOCAL_SDK_VERSION is not set

When LOCAL_SDK_VERSION is not set, frameworks.jar is put
in the classpath for javac.  If it is also in the classpath
(as opposed to the bootclasspath) for desugar then desugar
tries to rewrite classes that implement interfaces with
default methods to contain calls to the generated companion
classes for those interfaces.  frameworks.jar will not
contain the companion classes, which causes proguard to
fail.

Move frameworks.jar to the bootclasspath, which matches more
closely with builds against the SDK stubs jars.

Also remove the static libraries from the classpath, they have
already been merged into the input jar.

Test: m checkbuild
Change-Id: If30943efcaea44b2db1b38a6c1d558113324757f