FlatLatticeTiling: miscellaneous edits and cleanups

- In particular, remove commented XLALNearestFlatLatticePointToRandomPoints()
FlatLatticeTiling: fix bug in setting parameter-space bounds

- Due to copy-and-paste error 'phys_offset' was being used instead of 'point'
- Replace FLT_GetBounds() with FLT_SetBounds() which is hard-coded to use
  'point', 'lower', and 'upper' vectors to set bounds, which can then be
  accessed and used as needed
- Calculation of 'phys_offset' uses 'point', then copies result
- Breaks testCFSv2_FLTgrids.sh: gridType=8 test passes but not gridType=9, so
  skip test for now; also reduce the parameter space, and thus the file sizes
  of Fstat files generated by this test, for when test is re-enabled