modpost: remove is_vmlinux() call in check_for_{gpl_usage,unused}()

modpost: remove is_vmlinux() call in check_for_{gpl_usage,unused}()

check_exports() is never called for vmlinux because mod->skip is set
for vmlinux.

Hence, check_for_gpl_usage() and check_for_unused() are not called
for vmlinux, either. is_vmlinux() is always false here.

Remove the is_vmlinux() calls, and hard-code the ".ko" suffix.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>