remove automatic field propagation from `balance_statespace`

[baggepinnen]

The reason is that many abstract statespace types have fields that are affected by the balancing, and the automatic forwarding of those fields without application of the balancing led to incorrect answers. The proper way of handling this is for each type to implement their own method of balance_statespace if the additional fields are required.

[codecov[bot]]

Codecov Report

Merging #863 (fd2e732) into master (e9690d9) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #863   +/-   ##
=======================================
  Coverage   92.72%   92.72%           
=======================================
  Files           5        5           
  Lines         330      330           
=======================================
  Hits          306      306           
  Misses         24       24           

[JuliaControlBot]

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