Remove usage of fixtures in agg primitive tests

[kmax12]

This PR removes the usage of fixture in one of our test files. The usage of fixture didn’t simplify the code or encourage reusability, so they’ve been removed

[codecov]

Codecov Report

Merging #325 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master     #325      +/-   ##
==========================================
+ Coverage   95.12%   95.13%   +<.01%     
==========================================
  Files          71       71              
  Lines        7714     7702      -12     
==========================================
- Hits         7338     7327      -11     
+ Misses        376      375       -1

Impacted Files	Coverage Δ
...ools/tests/primitive_tests/test_direct_features.py	100% <ø> (ø)
...tools/tests/primitive_tests/test_primitive_base.py	97.36% <ø> (ø)
...s/tests/primitive_tests/test_transform_features.py	98.87% <ø> (ø)
...aturetools/tests/primitive_tests/test_agg_feats.py	99.06% <100%> (ø)

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[rwedge]

Looks good