scsitest is a SCSI target emulator used by one test, and has little
reason to get installed. Make the component private to the test using
it and obsolete the installed one.

IOW, rename sys/rump/dev

scsitest is a SCSI target emulator used by one test, and has little
reason to get installed. Make the component private to the test using
it and obsolete the installed one.

IOW, rename sys/rump/dev/lib/libscsitest -> tests/dev/scsipi/libscsitest

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