kgssapi: Remove broken MOD_UNLOAD code

[emaste]

Summary

The module panicked at unload with "recursing but non-recursive rw".
There is a comment that "Unloading of the kgssapi module is not
currently supported" so just #if 0 the code in the unload path.

PR:             291249
Fixes: ad704a34bc2c ("Use syscall_helper_register(9) rather than syscall_register().")

[rmacklem]

Looks fine to me.