Small cleanups in VEX: 
  * rm unused arm64 function
  * ijk_nodecode: always set the 4 components of the result
    (avoid a compiler warning that a part is not initialised)



git-svn-id: svn://svn.valgrind.org/vex/trunk@2919 8f6e269a-dfd6-0310-a8e1-e2731360e62c