Fix repo-transfer-and-team-repo-count bug

[ethantkoenig]

Remove code in TransferOwnership which decrements teams' number of repos, since that is already done by the removeOrgRepo(..) method. Also adds a unit test for a TransferOwnership.

[codecov-io]

Codecov Report

Merging #3241 into master will increase coverage by 0.27%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3241      +/-   ##
==========================================
+ Coverage   34.67%   34.95%   +0.27%     
==========================================
  Files         277      277              
  Lines       40014    40004      -10     
==========================================
+ Hits        13876    13982     +106     
+ Misses      24134    23982     -152     
- Partials     2004     2040      +36

Impacted Files	Coverage Δ
models/repo.go	43.39% <ø> (+1.92%)	⬆️
models/repo_indexer.go	50.97% <0%> (-0.98%)	⬇️
models/action.go	65.11% <0%> (+0.22%)	⬆️
models/repo_list.go	67.18% <0%> (+1.56%)	⬆️
models/lfs.go	28.26% <0%> (+2.17%)	⬆️
modules/lfs/server.go	35.01% <0%> (+14.32%)	⬆️
modules/lfs/content_store.go	43.75% <0%> (+35.93%)	⬆️

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[lunny]

LGTM

[lunny]

will fix #3233

[lafriks]

LGTM

[lafriks]

@ethantkoenig please backport