TEST: test_tck and test_trk conversion to pytest

[robbisg]

• Removed skip test
• Converted to pytest TEST: Drop nose for pytest #865 Sprint: Pytest conversion #864

[codecov]

Codecov Report

Merging #874 into pytest will increase coverage by 2.12%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           pytest     #874      +/-   ##
==========================================
+ Coverage   81.33%   83.46%   +2.12%     
==========================================
  Files          97       97              
  Lines       12408    12427      +19     
  Branches     2187     2195       +8     
==========================================
+ Hits        10092    10372     +280     
+ Misses       1900     1686     -214     
+ Partials      416      369      -47     

Impacted Files	Coverage Δ
nibabel/pydicom_compat.py	63.63% <0.00%> (-22.73%)	⬇️
nibabel/filename_parser.py	92.04% <0.00%> (-2.28%)	⬇️
nibabel/optpkg.py	93.10% <0.00%> (+3.35%)	⬆️
nibabel/streamlines/tractogram_file.py	100.00% <0.00%> (+5.00%)	⬆️
nibabel/streamlines/trk.py	94.62% <0.00%> (+16.45%)	⬆️
nibabel/streamlines/tck.py	99.46% <0.00%> (+19.78%)	⬆️
nibabel/streamlines/tractogram.py	99.67% <0.00%> (+24.75%)	⬆️
nibabel/streamlines/array_sequence.py	99.30% <0.00%> (+34.96%)	⬆️

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[effigies]

LGTM. Feel free to merge if Travis passes.

[effigies]

Travis failed but not for reasons related to this PR. I'll go ahead and merge.