kde-neon-extension: remove extra build environment variables that are…

[ScarlettGatelyMoore]

… causing build failures.

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• Have you successfully run pytest tests/unit?

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These build env variables are causing builds to fail in weird ways. Just remove them and let snapcrafters set them themselves.

[codecov-commenter]

Codecov Report

Merging #4193 (238bcc6) into main (d8930f1) will not change coverage.
The diff coverage is n/a.

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@@           Coverage Diff           @@
##             main    #4193   +/-   ##
=======================================
  Coverage   93.90%   93.90%           
=======================================
  Files         569      569           
  Lines       43746    43746           
=======================================
  Hits        41078    41078           
  Misses       2668     2668           

Impacted Files	Coverage Δ
snapcraft/extensions/kde_neon.py	100.00% <ø> (ø)
tests/unit/extensions/test_kde_neon.py	100.00% <ø> (ø)

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[MirkoFerrati]

I tested this here canonical/gazebo_snap@06d1e77 and it worked as expected, compared with snapcore:main branch where it fails in the build stage due to pkgconfig errors.
But I cannot guarantee it will work for all use-cases, the snapcraft.yaml I am using is quite complex and may hide corner cases.

[MirkoFerrati]

@ScarlettGatelyMoore @lengau could one of you fix the out-of-date so this can be merged?

[ScarlettGatelyMoore]

@ScarlettGatelyMoore @lengau could one of you fix the out-of-date so this can be merged?

done