Remove AMDGPU extension

[vchuravy]

The AMDGPU extension was perhaps to ambitious we first need support for Symbols (JuliaGPU/AMDGPU.jl#796),
and thus it is currently untested and unused.

x-ref: #2478 (comment)

[github-actions]

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.68%. Comparing base (c9d975f) to head (2298a53).
Report is 2 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2485       +/-   ##
===========================================
+ Coverage   26.15%   96.68%   +70.53%     
===========================================
  Files         507      506        -1     
  Lines       41848    42005      +157     
===========================================
+ Hits        10943    40609    +29666     
+ Misses      30905     1396    -29509     

Flag	Coverage Δ
unittests	96.68% <ø> (+70.53%)	⬆️

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[ranocha]

Thanks