2 copies of taskcall.c removed

2 copies of taskcall.c removed

- taskcall.c is 3x in the trunk as part of libc, libsysutil and
  libsys.  It should be only part of libsys.

- only system process should be linked with libsys, therefore using
  raw _taskcall() in service.c is replaced by _syscall()

- the same for minix_rs.c

- lib/other/sys_eniop.c can go without replacement as it is part of
  syslib