Remove SVR2 support
SVR2 was obsolete by 1986 and is no longer supported by anybody, and its
code was getting in the way of use of this module by Emacs, which has
its own 'read' function anyway.
* src/filemanager/mountlist.c: remove SVR2-specific code.
* m4.include/fsusage.m4: do not test for sys/filsys.h or set
STAT_READ_FILSYS.
Signed-off-by: Andrew Borodin <aborodin@vmail.ru>