Code cleanup: drop 'request' argument from async fixtures

[asvetlov]

The fixture injection is not needed, pytest 6.1.0+ works fine with using request argument from pytest_fixture_setup() hook.

[codecov-commenter]

Codecov Report

Merging #270 (43cbb6f) into master (4353327) will decrease coverage by 0.08%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #270      +/-   ##
==========================================
- Coverage   92.45%   92.36%   -0.09%     
==========================================
  Files           3        3              
  Lines         265      262       -3     
  Branches       34       34              
==========================================
- Hits          245      242       -3     
  Misses         13       13              
  Partials        7        7              

Impacted Files	Coverage Δ
plugin.py	92.21% <0.00%> (-0.09%)	⬇️

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[seifertm]

Good find!

[asvetlov]

@seifertm thanks!
To be clear, fixtredef.addfinalizer() does the same work. Actually, request.addfinalizer() calls fixturedef.addfinalizer() internally.