remove wavelength from vapp

[syhaffert]

quick fix for issue #63 .

[codecov]

Codecov Report

Merging #64 into master will not change coverage.
The diff coverage is 50%.

@@           Coverage Diff           @@
##           master      #64   +/-   ##
=======================================
  Coverage   74.64%   74.64%           
=======================================
  Files          92       92           
  Lines        5718     5718           
=======================================
  Hits         4268     4268           
  Misses       1450     1450

Impacted Files	Coverage Δ
hcipy/coronagraphy/apodizing_phase_plate.py	43.85% <50%> (ø)	⬆️

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