linux(4): Get rid of the opt_compat.h include.
Since e013e369 COMPAT_LINUX, COMPAT_LINUX32 build options are removed,
so include of opt_compat.h is no more needed.
MFC after: 2 weeks
(cherry picked from commit 10d16789a383a5b9e007dfd4c2e7844e044eaf7d)