maintainer: Removed metadynamics

[fweik]

Closes #1142.

Description of changes:

• Removed metadynamics feature

This can be better done from the front end and very similar functionality
is implemented in the reaction ensemble. Also undocumented and unused
since years because it does not have an interface.

[jonaslandsgesell]

Hi Flo,

very similar functionality is implemented in the reaction ensemble

This is true in the sense of this paper from Christoph Junghans und Danny Perez: https://pubs.acs.org/doi/10.1021/ct500077d

The Wang-Landau algorithm is so to say the Metadynamics of Monte-Carlo methods.

Regarding the MD-Metadynamics implementation I don't know how well it was tested, so it seems fine to remove it.

[codecov]

Codecov Report

Merging #3563 into python will increase coverage by 0%.
The diff coverage is n/a.

@@          Coverage Diff           @@
##           python   #3563   +/-   ##
======================================
  Coverage      87%     88%           
======================================
  Files         525     524    -1     
  Lines       23614   23564   -50     
======================================
+ Hits        20726   20765   +39     
+ Misses       2888    2799   -89     

Impacted Files	Coverage Δ
src/core/nonbonded_interactions/gay_berne.hpp	97% <0%> (-2%)	⬇️
src/core/grid.hpp	100% <0%> (ø)	⬆️
src/core/nonbonded_interactions/gay_berne.cpp	100% <0%> (ø)	⬆️
src/core/particle_data.cpp	96% <0%> (+<1%)	⬆️
src/core/grid_based_algorithms/lb.cpp	96% <0%> (+<1%)	⬆️
...re/bonded_interactions/bonded_interaction_data.cpp	91% <0%> (+2%)	⬆️
src/core/electrostatics_magnetostatics/dipole.cpp	63% <0%> (+5%)	⬆️
...rc/core/electrostatics_magnetostatics/scafacos.cpp	70% <0%> (+5%)	⬆️
src/core/global.cpp	83% <0%> (+7%)	⬆️

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[jngrad]

Regarding the MD-Metadynamics implementation I don't know how well it was tested

It has no test.