Remove header magic

[Anaphory]

Fixes #356

[codecov]

Codecov Report

Merging #357 (be5937f) into master (b2bfdf1) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #357   +/-   ##
=======================================
  Coverage   80.78%   80.78%           
=======================================
  Files          43       43           
  Lines        4305     4305           
  Branches     1080     1081    +1     
=======================================
  Hits         3478     3478           
  Misses        633      633           
  Partials      194      194           

Impacted Files	Coverage Δ
src/lexedata/util/excel.py	90.00% <ø> (-0.09%)	⬇️
src/lexedata/importer/excel_long_format.py	89.49% <100.00%> (+0.14%)	⬆️

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