Remove librpma engine as librpma library is no longer maintained

[grom72]

Remove librpma engines as the librpma library project has been archived on GitHub.

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Reminders:

1. If you modify struct thread_options, also make corresponding changes in cconv.c and bump FIO_SERVER_VER in server.h
2. If you change the ioengine interface (hooks, flags, etc), remember to bump FIO_IOOPS_VERSION in ioengines.h.