Remove code with alpha1/2 to fix failing tests

[bennibolm]

In trixi-framework/Trixi.jl#2588, I removed alpha1 and alpha2. Now, everything is directly done with alpha.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.32%. Comparing base (1b0d2f5) to head (9a5fa0e).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #116      +/-   ##
==========================================
- Coverage   99.33%   99.32%   -0.00%     
==========================================
  Files          87       87              
  Lines        4600     4587      -13     
==========================================
- Hits         4569     4556      -13     
  Misses         31       31              

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[DanielDoehring]

Apologies from my side if my merge of #2588 caused this (although tests where passing back then)

[bennibolm]

Apologies from my side if my merge of #2588 caused this (although tests where passing back then)

I also didn't think about that. There was no upstream test for subcell limiting in TrixiShallowWater.jl back then. But my changes still were breaking in some sense.
Hopefully, there will be no problems anymore with the new test.

[patrickersing]

LGTM!
Thanks a lot for fixing this.