mksyscall.pl, types_linux.go: regenerate linux {386,amd64} files

Import syscall so that Kill can refer to syscall.Signal.  Drop
termios constants from types_linux.go--all other systems get
them from mkerrors.sh.

Fixes golang/go#8865.

LGTM=r
R=r
CC=golang-codereviews
https://golang.org/cl/152980044

unix/mksyscall.pl

@@ -304,7 +304,12 @@ print <<EOF;
 
 package unix
 
-import "unsafe"
+import (
+	"syscall"
+	"unsafe"
+)
+
+var _ syscall.Errno
 
 $text
 EOF