Remove solve_triu and solve_triu_left for RingElem

[joschmitt]

Let's see whether something breaks.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 86.95%. Comparing base (a49b43f) to head (8e82bab).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1661      +/-   ##
==========================================
+ Coverage   86.92%   86.95%   +0.02%     
==========================================
  Files         115      115              
  Lines       29692    29653      -39     
==========================================
- Hits        25810    25784      -26     
+ Misses       3882     3869      -13     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[joschmitt]

What does this Aqua failure persistent tasks tell me? https://github.com/Nemocas/AbstractAlgebra.jl/actions/runs/8629741451/job/23654590525?pr=1661
I skimmed https://juliatesting.github.io/Aqua.jl/dev/persistent_tasks/#Persistent-Tasks and I have no idea how this pull request could have affected this.

[thofma]

oscar-system/Oscar.jl#3576

[joschmitt]

Looks like nobody is gonna miss these functions.