kern/intr: remove support for passing trap frame as argument

While otherwise a handy potential approach, getting the trap frame via
the argument isn't documented and isn't supposed to be used. With all
uses removed, now remove support to end the mixed calling conventions.

Differential Revision: https://reviews.freebsd.org/D37688

Reviewed by: imp, mhorne
Pull Request: https://github.com/freebsd/freebsd-src/pull/1225