x86emu: remove localy added __FBSDID
This partially reverts 0a2e9846fdf3f3d42a9ee65d0d8669f6be11c879.
Reviewed by: imp, delphij
Differential Revision: https://reviews.freebsd.org/D42705
(cherry picked from commit 3faba3002f466e1bdad4767c55257e04433ee96b)