Correct generate_ororgraphic_smoothing_coefficients doc-string

[brhooper]

As an IMPROVER scientist, I like it when equations in doc-strings accurately represent the actual calculations being carried out, rather than bamboozling me.

This (ancient surprisingly young) PR changed the generate_orographic_smoothing_coefficients method so that it no longer required a coefficient to be specified, but rather normalised the calculated smoothing coefficients between user specified min and max values. The plugin doc-strings were updated accordingly, but a vestigial reference to a coefficient in the CLI doc-string remains. This PR removes that reference.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.41%. Comparing base (84a8944) to head (3a3de5f).
Report is 6 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1999      +/-   ##
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+ Coverage   98.39%   98.41%   +0.01%     
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  Files         124      124              
  Lines       12212    12337     +125     
==========================================
+ Hits        12016    12141     +125     
  Misses        196      196              

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[bayliffe]

This PR has a lot of attitude, which makes it stand out in a crowd. The author has requested a review from someone he has implicitly called "ancient" in his description, which seems quite bold 👴