chore(metrics) drop 'mid' argument from ngx_wa_metrics_histogram_record

[casimiro]

The argument was only used when logging the histogram in debug mode. Since our tests don't assert on the actual value of 'mid', we don't really need to have it printed in logs.

Also, ngx_wa_metrics_record already prints the mid of the metric being updated.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.83363%. Comparing base (3bb2f15) to head (8485b29).
Report is 2 commits behind head on main.

Additional details and impacted files

@@              Coverage Diff              @@
##                main        #617   +/-   ##
=============================================
  Coverage   90.83363%   90.83363%           
=============================================
  Files             52          52           
  Lines          11204       11204           
=============================================
  Hits           10177       10177           
  Misses          1027        1027           

Files with missing lines	Coverage Δ
src/common/metrics/ngx_wa_histogram.c	99.35484% <100.00000%> (ø)
src/common/metrics/ngx_wa_metrics.c	92.21790% <100.00000%> (ø)
src/common/metrics/ngx_wa_metrics.h	100.00000% <ø> (ø)

... and 2 files with indirect coverage changes

Flag	Coverage Δ
unit	90.57160% <100.00000%> (-0.01018%)	⬇️
valgrind	82.51447% <100.00000%> (+0.06865%)	⬆️

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[thibaultcha]

Nice, always nice to keep things tidy!