Don't export TrixiBase

[efaulhaber]

Sorry, I know I'm a little late to the party, but why do we export TrixiBase? Wouldn't it suffice to just export trixi_include?

Originally posted by @sloede in #1832 (comment)

[github-actions]

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[sloede]

Thanks!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (4f33837) 96.38% compared to head (64352e0) 96.38%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1846   +/-   ##
=======================================
  Coverage   96.38%   96.38%           
=======================================
  Files         455      455           
  Lines       36336    36336           
=======================================
  Hits        35019    35019           
  Misses       1317     1317           

Flag	Coverage Δ
unittests	96.38% <ø> (ø)

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