Remove deprecated Scene3d plugin

[chapulina]

• Follow up to Split transport scene manager into a plugin outside Scene3D #221

Summary

Scene3D is deprecated on Fortress (tick), now we remove it on Garden (tock).

Checklist

• Signed all commits for DCO
• Added tests
• Added example and/or tutorial
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed (See contributing)
• All tests passed (See test coverage)
• While waiting for a review on your PR, please help review another open pull request to support the maintainers

Note to maintainers: Remember to use Squash-Merge and edit the commit message to match the pull request summary while retaining Signed-off-by messages.

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[ahcorde]

ouh yes!

[codecov]

Codecov Report

Merging #438 (f9ad2d4) into main (02cb9fd) will increase coverage by 2.40%.
The diff coverage is 69.64%.

@@            Coverage Diff             @@
##             main     #438      +/-   ##
==========================================
+ Coverage   64.07%   66.47%   +2.40%     
==========================================
  Files          45       44       -1     
  Lines        5539     4740     -799     
==========================================
- Hits         3549     3151     -398     
+ Misses       1990     1589     -401     

Impacted Files	Coverage Δ
include/gz/gui/GuiEvents.hh	100.00% <ø> (ø)
include/gz/gui/Helpers.hh	77.77% <ø> (ø)
include/gz/gui/Plugin.hh	100.00% <ø> (ø)
src/Application.cc	84.82% <ø> (ø)
src/gz.cc	42.85% <ø> (ø)
src/plugins/camera_tracking/CameraTracking.cc	68.45% <ø> (ø)
src/plugins/grid_config/GridConfig.cc	22.35% <ø> (ø)
src/plugins/grid_config/GridConfig.hh	100.00% <ø> (ø)
src/plugins/minimal_scene/MinimalScene.hh	100.00% <ø> (ø)
src/plugins/minimal_scene/MinimalSceneRhi.cc	0.00% <0.00%> (ø)
... and 7 more

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