Use write_table for image statistics

[maxnoe]

This was the last table in dl1 output that was still using the astropy mechanism. As of now, we don't have any table_column_meta tables in the output

[kosack]

Great!

[codecov]

Codecov Report

Merging #1863 (69b0c81) into master (2923760) will decrease coverage by 0.21%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #1863      +/-   ##
==========================================
- Coverage   92.32%   92.10%   -0.22%     
==========================================
  Files         191      188       -3     
  Lines       15395    14768     -627     
==========================================
- Hits        14213    13602     -611     
+ Misses       1182     1166      -16     

Impacted Files	Coverage Δ
ctapipe/tools/dl1_merge.py	83.33% <100.00%> (+1.13%)	⬆️
ctapipe/tools/process.py	93.02% <100.00%> (ø)
ctapipe/utils/filelock.py	75.00% <0.00%> (-25.00%)	⬇️
ctapipe/visualization/bokeh.py	73.52% <0.00%> (-19.46%)	⬇️
ctapipe/utils/rgbtohex.py	83.33% <0.00%> (-16.67%)	⬇️
ctapipe/visualization/tests/test_bokeh.py	98.61% <0.00%> (-1.39%)	⬇️
ctapipe/io/eventsource.py	93.00% <0.00%> (-1.00%)	⬇️
ctapipe/visualization/mpl_camera.py	92.30% <0.00%> (-0.08%)	⬇️
ctapipe/tools/tests/test_tools.py	100.00% <0.00%> (ø)
ctapipe/plotting/bokeh_event_viewer.py
... and 4 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2923760...69b0c81. Read the comment docs.