tests: remove arch_triplet from unit test

[mr-cal]

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Minor fix for unit tests.

Two PRs (1 and 2) touched the same unit test file. One removed all references to arch_triplet and the other added 2 more tests with arch_triplet still present.

[codecov-commenter]

Codecov Report

Merging #4160 (0ceea7a) into main (e52221b) will increase coverage by 0.04%.
The diff coverage is 100.00%.

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@@            Coverage Diff             @@
##             main    #4160      +/-   ##
==========================================
+ Coverage   94.80%   94.85%   +0.04%     
==========================================
  Files         648      648              
  Lines       54294    54353      +59     
==========================================
+ Hits        51475    51554      +79     
+ Misses       2819     2799      -20     

Impacted Files	Coverage Δ
snapcraft/elf/elf_utils.py	95.38% <100.00%> (+0.07%)	⬆️
snapcraft/meta/snap_yaml.py	96.63% <100.00%> (+0.01%)	⬆️
snapcraft/parts/lifecycle.py	92.90% <100.00%> (+4.19%)	⬆️
snapcraft/projects.py	96.12% <100.00%> (+0.05%)	⬆️
snapcraft/utils.py	91.57% <100.00%> (+0.09%)	⬆️
tests/unit/elf/test_elf_utils.py	100.00% <100.00%> (ø)
tests/unit/linters/test_classic_linter.py	100.00% <100.00%> (ø)
tests/unit/linters/test_library_linter.py	100.00% <100.00%> (ø)
tests/unit/linters/test_linters.py	100.00% <100.00%> (ø)
tests/unit/meta/test_snap_yaml.py	100.00% <100.00%> (ø)
... and 3 more

... and 1 file with indirect coverage changes

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