rm old reaction ensemble tutorial

[jonaslandsgesell]

No description provided.

[codecov]

Codecov Report

Merging #3255 into python will decrease coverage by <1%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           python   #3255   +/-   ##
======================================
- Coverage      85%     85%   -1%     
======================================
  Files         531     531           
  Lines       25796   25796           
======================================
- Hits        22169   22168    -1     
- Misses       3627    3628    +1

Impacted Files	Coverage Δ
src/core/electrostatics_magnetostatics/p3m.cpp	86% <0%> (-1%)	⬇️

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