bhyve/vioapic: remove an extra pin masked check

vioapic_send_intr does already check whether the pin is masked before
injecting the interrupt, there's no need to do it in vioapic_write
also.

No functional change intended.

Reviewed by: grehan
Differential revision: https://reviews.freebsd.org/D28236

(cherry picked from commit 49429cf9be7f43c37723175f90c56b29e29d1680)