Revert some changes from #255

[dnerini]

Some changes that were meant for #254 were wrongly included in #255. This PR tries to revert them.

[aperezhortal]

Good catch! It looks to go after the tests passed.

[codecov]

Codecov Report

Merging #271 (ca57193) into master (8a65727) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #271      +/-   ##
==========================================
+ Coverage   82.22%   82.23%   +0.01%     
==========================================
  Files         158      158              
  Lines       12088    12100      +12     
==========================================
+ Hits         9939     9951      +12     
  Misses       2149     2149              

Flag	Coverage Δ
unit_tests	82.23% <100.00%> (+0.01%)	⬆️

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Impacted Files	Coverage Δ
pysteps/tests/helpers.py	94.28% <ø> (ø)
pysteps/utils/reprojection.py	87.87% <ø> (ø)
pysteps/io/importers.py	72.03% <100.00%> (+0.48%)	⬆️

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