remove unused example param validation

[olegpidsadnyi]

The validation doesn't seem to be practical.
Sometimes you just want to comment out a step and reformatting the entire example table is too tedious.

[codecov]

Codecov Report

Merging #499 (5bdeee6) into master (d4f74d2) will decrease coverage by 0.09%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #499      +/-   ##
==========================================
- Coverage   95.49%   95.40%   -0.10%     
==========================================
  Files          48       48              
  Lines        1577     1566      -11     
  Branches      170      166       -4     
==========================================
- Hits         1506     1494      -12     
- Misses         44       45       +1     
  Partials       27       27              

Impacted Files	Coverage Δ
pytest_bdd/exceptions.py	100.00% <ø> (ø)
pytest_bdd/hooks.py	100.00% <ø> (ø)
pytest_bdd/parser.py	97.40% <ø> (-0.58%)	⬇️
pytest_bdd/scenario.py	91.01% <ø> (-0.06%)	⬇️
tests/feature/test_outline.py	100.00% <100.00%> (ø)

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