Remove the geodesic regression tutorial.

[kellertuer]

cf. #427.

Since the tutorial is wrong – and was one of the last once illustrating (just) an application, it is removed.
When someone finds time and fixes the bugs – this could be readied, but then to ManoptExamples.jl

Tutorials here should focus on features and how to accomplish several features – not concrete examples, especially not as advances as ton the tangent bundle.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.90%. Comparing base (2aa8f62) to head (1e07f34).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #430   +/-   ##
=======================================
  Coverage   99.90%   99.90%           
=======================================
  Files          78       78           
  Lines        8289     8289           
=======================================
  Hits         8281     8281           
  Misses          8        8           

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