remove presys.h and postsys.h

Both files are nearly identical to prewin.h and postwin.h

Change-Id: I1f45e46dfcc00043a9e2df82e0070cd1b976c4af
Reviewed-on: https://gerrit.libreoffice.org/9294
Reviewed-by: Thomas Arnhold <thomas@arnhold.org>
Tested-by: Thomas Arnhold <thomas@arnhold.org>