Doc corrections to LD stats and simulation

[hyanwong]

Here are two separate commits, one that points out that some simulators can keep non-coalescent nodes, the other removing the reference to the deprecated LDCalculator.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.68%. Comparing base (0e38fc3) to head (5fe7119).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #3491   +/-   ##
=======================================
  Coverage   91.68%   91.68%           
=======================================
  Files          38       38           
  Lines       32232    32232           
  Branches     5153     5153           
=======================================
  Hits        29553    29553           
  Misses       2346     2346           
  Partials      333      333           

Flag	Coverage Δ
C	82.23% <ø> (ø)
c-python	77.56% <ø> (ø)
python-tests	96.44% <ø> (ø)
python-tests-no-jit	33.30% <ø> (ø)

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Components	Coverage Δ
Python API	98.73% <ø> (ø)
Python C interface	91.25% <ø> (ø)
C library	91.24% <ø> (ø)

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