Ensure delete user deletes all comments

[lunny]

There is a mistake in the batched delete comments part of DeleteUser which causes some comments to not be deleted

The code incorrectly updates the start of the limit clause resulting in most comments not being deleted.

			if err = e.Where("type=? AND poster_id=?", issues_model.CommentTypeComment, u.ID).Limit(batchSize, start).Find(&comments); err != nil {

should be:

			if err = e.Where("type=? AND poster_id=?", issues_model.CommentTypeComment, u.ID).Limit(batchSize, 0).Find(&comments); err != nil {

[zeripath]

The DeleteComment code is really quite inefficient, especially the neuter cross-references code. This really should all be done within the DB. There is no need to get this stuff out of the DB.

[zeripath]

Approved as this fixes a serious bug - but see my comment about the serious inefficiencies in this code.

[codecov-commenter]

Codecov Report

Merging #21067 (4a6c96e) into main (b42aaf2) will decrease coverage by 0.09%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main   #21067      +/-   ##
==========================================
- Coverage   47.13%   47.03%   -0.10%     
==========================================
  Files        1008     1007       -1     
  Lines      137718   137581     -137     
==========================================
- Hits        64911    64716     -195     
- Misses      64870    64935      +65     
+ Partials     7937     7930       -7     

Impacted Files	Coverage Δ
models/user.go	32.84% <0.00%> (ø)
modules/sync/status_pool.go	64.00% <0.00%> (-36.00%)	⬇️
services/user/user.go	17.36% <0.00%> (-30.00%)	⬇️
modules/process/manager_exec.go	58.13% <0.00%> (-27.91%)	⬇️
modules/context/xsrf.go	78.04% <0.00%> (-14.64%)	⬇️
modules/secret/secret.go	52.00% <0.00%> (-12.00%)	⬇️
modules/charset/escape_stream.go	58.68% <0.00%> (-8.93%)	⬇️
modules/util/filebuffer/file_backed_buffer.go	52.50% <0.00%> (-6.25%)	⬇️
modules/charset/charset.go	71.73% <0.00%> (-2.18%)	⬇️
modules/log/file.go	68.78% <0.00%> (-1.92%)	⬇️
... and 6 more

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