Drop requirements files, attempt to run "setup.py install" in rtd

[juhoinkinen]

Remove unnecessary ´requirements` files and a package for their creation.

[codecov]

Codecov Report

Merging #285 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #285   +/-   ##
=======================================
  Coverage   99.31%   99.31%           
=======================================
  Files          52       52           
  Lines        2624     2624           
=======================================
  Hits         2606     2606           
  Misses         18       18

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[osma]

Is this working properly? Can it be merged now?

[juhoinkinen]

Yes, now this is working and mergable. There were some randomish problems about builds failing, but adding the .readthedocs.yml seems to solve those (using the same settings via RTD webpage worked from time to time).

For future reference: Wiping build environment in RTD can help to solve some problems

(Also, the .rst files can be removed from version control as they can automatically generated: #287.)