fix for bug 8456

On systems without bundled johntheripper (either by removing the bundled version or by no compatible version shipped) the system john is used.  In this case, all of the checking for compatible bundled jtr makes no sense and as such we can shortcut out of this to not only reduce the size of msf (for embedded) but also to speed execution (saving multiple calls to some random bundled binary cpuinfo*.bin).

This patch makes it very easy to simply remove cpuinfo and msf will not try to run it when missing and default to running john from the path.