Drop User Burn Support

[8marz8]

Description

Removing UserBurnSupportOp definition and usage throughout the codebase as it's not fully implemented and used.

Applicable issues

• closes #4071

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 83.41%. Comparing base (577b118) to head (7a83433).

Additional details and impacted files

@@            Coverage Diff             @@
##             next    #4378      +/-   ##
==========================================
- Coverage   83.44%   83.41%   -0.03%     
==========================================
  Files         449      448       -1     
  Lines      325514   323911    -1603     
==========================================
- Hits       271632   270199    -1433     
+ Misses      53882    53712     -170     

Files	Coverage Δ
stackslib/src/burnchains/burnchain.rs	81.88% <100.00%> (+0.24%)	:arrow_up:
stackslib/src/burnchains/tests/burnchain.rs	99.87% <100.00%> (+0.08%)	:arrow_up:
stackslib/src/burnchains/tests/mod.rs	94.08% <100.00%> (+0.25%)	:arrow_up:
stackslib/src/chainstate/burn/db/processing.rs	87.39% <ø> (-0.01%)	:arrow_down:
stackslib/src/chainstate/burn/db/sortdb.rs	91.86% <100.00%> (-0.22%)	:arrow_down:
stackslib/src/chainstate/burn/distribution.rs	95.88% <ø> (-0.95%)	:arrow_down:
stackslib/src/chainstate/burn/mod.rs	94.44% <ø> (+0.24%)	:arrow_up:
.../chainstate/burn/operations/leader_block_commit.rs	96.08% <ø> (ø)
.../chainstate/burn/operations/leader_key_register.rs	97.27% <ø> (ø)
stackslib/src/chainstate/burn/operations/mod.rs	62.44% <ø> (+2.83%)	:arrow_up:
... and 18 more

... and 20 files with indirect coverage changes

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[8marz8]

@jcnelson @kantai Should "StagingUserBurnSupport" also be deleted?

[jcnelson]

Also, yes -- feel free to remove StagingUserBurnSupport. As long as CI passes, it should be fine.