compactor: clean up

[gyuho]

Separate clean up changes from #9474.

[codecov-io]

Codecov Report

Merging #9476 into master will decrease coverage by 0.25%.
The diff coverage is 79.16%.

@@            Coverage Diff            @@
##           master   #9476      +/-   ##
=========================================
- Coverage   72.96%   72.7%   -0.26%     
=========================================
  Files         364     364              
  Lines       30883   30887       +4     
=========================================
- Hits        22533   22457      -76     
- Misses       6749    6812      +63     
- Partials     1601    1618      +17

Impacted Files	Coverage Δ
compactor/compactor.go	0% <ø> (ø)	⬆️
compactor/revision.go	79.54% <75%> (+10.49%)	⬆️
compactor/periodic.go	83.33% <83.33%> (+8.33%)	⬆️
clientv3/integration/util.go	66.66% <0%> (-33.34%)	⬇️
pkg/transport/timeout_conn.go	80% <0%> (-20%)	⬇️
pkg/adt/interval_tree.go	82.28% <0%> (-11.72%)	⬇️
proxy/grpcproxy/watcher.go	85.71% <0%> (-8.17%)	⬇️
pkg/tlsutil/tlsutil.go	86.2% <0%> (-6.9%)	⬇️
clientv3/namespace/watch.go	72.72% <0%> (-6.07%)	⬇️
etcdctl/ctlv3/command/lease_command.go	65.34% <0%> (-5.95%)	⬇️
... and 10 more

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