module: icp: rip out the Solaris loadable module architecture

After progressively folding away null cases, it turns out there's
/literally/ nothing there, even if some things are part of the
Solaris SPARC DDI/DKI or the seventeen module types (some doubled for
32-bit userland), or the entire modctl syscall definition.
Nothing.

Initialisation is handled in illumos-crypto.c,
which calls all the initialisers directly

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Attila Fülöp <attila@fueloep.org>
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Closes #12895
Closes #12902