Remove bootclasspath handling for Jack

Bootclasspath libraries are already added in LOCAL_JAVA_LIBRARIES by
java.mk and host_dalvik_java_library.mk meaning that bootclasspath
handling was just doing a duplicate work and adding duplicated entries
to the classpath.

Also fix order of bootclasspath libraries for host.

Bug: 28307907
Change-Id: I6e98fc651a127435c029de65285dbf2cb04844af