iser: Remove redundant linuxkpi MODULE_DEPEND

Since ibcore depends on linuxkpi, there is no need to pull in the
linuxkpi dependency in iser.

Sponsored by: The FreeBSD Foundation
Reviewed by: trasz
Differential Revision: https://reviews.freebsd.org/D32977

(cherry picked from commit f7523c8a19d008412ccc969b12eeb756613f3678)