remove custom log message editing (closes #1545)

[petrelharp]

I looked at this a fair bit, and tried to figure out why the LogRecord object that previously had non-empty args now has empty logs, and also how to have a unit test for this, but didn't manage to on both counts.

On the other hand, I don't actually think this code was actually doing anything:

$ python3 -m stdpopsim -e slim --slim-scaling-factor 10 HomSap -c chr22 --left 10000000 --right 10010000 -o foo1.ts -d Africa_1T12 AFR:100
Simulation information:
    Engine: slim (4.1)
    Model id: Africa_1T12
    Model description: African population
    Population: number_samples (sampling_time_generations):
        AFR: 100 (0)
Contig Description:
    Contig origin: chr22:10000000-10010000
    Contig length: 10000.0
    Contig ploidy: 2
    Mean recombination rate: 2.1057233894035443e-08
    Mean mutation rate: 2.36e-08
    Genetic map: None

WARNING: /home/peter/projects/popsim-consortium/stdpopsim/stdpopsim/slim_engine.py:1602: SLiMScalingFactorWarning: You're using a scaling factor (10.0). This should give similar results for many situations, but is not equivalent, especially in the presence of selection. When using rescaling, you should be careful---do checks and compare results across different values of the scaling factor.
  warnings.warn(

WARNING: /home/peter/projects/tskit-dev/treestuff_venv/lib/python3.11/site-packages/msprime/ancestry.py:831: TimeUnitsMismatchWarning: The initial_state has time_units=ticks but time is measured in generations in msprime. This may lead to significant discrepancies between the timescales. If you wish to suppress this warning, you can use, e.g., warnings.simplefilter('ignore', msprime.TimeUnitsMismatchWarning)
  warnings.warn(message, TimeUnitsMismatchWarning)

The odd "warnings.warn(" lines are merely printing the line in the source code where the warning is raised, but the code was not removing that entirely.

[petrelharp]

Arrrgh.

[petrelharp]

This should work after #1553 goes in.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 99.83%. Comparing base (6926072) to head (2ad99df).

Files	Patch %	Lines
stdpopsim/cli.py	66.66%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1550   +/-   ##
=======================================
  Coverage   99.83%   99.83%           
=======================================
  Files         131      131           
  Lines        4333     4334    +1     
  Branches      594      595    +1     
=======================================
+ Hits         4326     4327    +1     
  Misses          3        3           
  Partials        4        4           

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