Simplified non-overlap condition

src/USER-DIFFRACTION/fix_saed_vtk.cpp

src/USER-MISC/fix_ave_spatial_sphere.cpp

src/USER-REAXC/fix_reaxc_species.cpp

src/fix_ave_atom.cpp

src/fix_ave_chunk.cpp

src/fix_ave_histo.cpp

src/fix_ave_spatial.cpp

src/fix_ave_time.cpp