Switch to FastCholesky.jl

[bvdmitri]

This PR removes the cholesky folder and uses FastCholesky instead

[bartvanerp]

Simplified distributions/wishart_inverse.jl slightly. If tests pass, feel free to merge.

[codecov]

Codecov Report

All modified lines are covered by tests ✅

Comparison is base (fcfc9c1) 67.24% compared to head (5879d6b) 67.33%.
Report is 9 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #354      +/-   ##
==========================================
+ Coverage   67.24%   67.33%   +0.09%     
==========================================
  Files         209      208       -1     
  Lines        7699     7654      -45     
==========================================
- Hits         5177     5154      -23     
+ Misses       2522     2500      -22     

Files	Coverage Δ
src/ReactiveMP.jl	63.15% <ø> (ø)
src/distributions/wishart_inverse.jl	84.84% <100.00%> (ø)

... and 4 files with indirect coverage changes

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