MAINT: Cython lint

[tylerjereddy]

I saw cython-lint used successfully upstream and ran it on MDAnalysis out of curiosity (below). Maybe some straightforward fixups we could accept.

cython-lint MDAnalysis/lib/*.pyx MDAnalysis/coordinates/*.pyx MDAnalysis/analysis/encore/*.pyx

MDAnalysis/lib/c_distances.pyx:38:24: 'fabs' imported but unused
MDAnalysis/lib/c_distances.pyx:299:17: 'j' defined but unused
MDAnalysis/coordinates/timestep.pyx:130:24: 'asiterable' imported but unused
MDAnalysis/coordinates/timestep.pyx:131:30: 'auxreader' imported but unused
MDAnalysis/coordinates/timestep.pyx:132:30: 'AuxReader' imported but unused
MDAnalysis/coordinates/timestep.pyx:133:16: 'units' imported but unused
MDAnalysis/coordinates/timestep.pyx:135:5: '_READERS' imported but unused
MDAnalysis/coordinates/timestep.pyx:135:15: '_READER_HINTS' imported but unused
MDAnalysis/coordinates/timestep.pyx:136:5: '_SINGLEFRAME_WRITERS' imported but unused
MDAnalysis/coordinates/timestep.pyx:137:5: '_MULTIFRAME_WRITERS' imported but unused
MDAnalysis/coordinates/timestep.pyx:138:5: '_CONVERTERS' imported but unused
MDAnalysis/coordinates/timestep.pyx:142:21: 'bool' imported but unused
MDAnalysis/coordinates/timestep.pyx:143:26: 'int64_t' imported but unused
MDAnalysis/coordinates/timestep.pyx:144:8: 'cython' imported but unused

[hmacdope]

:sweat_smile: oops, timestep.pyx is my fault.

[shalearkane]

Can you assign me this issue?

[hmacdope]

MDAnalysis/coordinates/timestep.pyx:132:30: 'AuxReader' imported but unused

@shalearkane you are free to work in this if you want. Have a look at our contributing guide and make a PR. Ping me if you are having any trouble.