go/oasis-node: Remove the debug dummy sub-commands

[Yawning]

Fixes #1471

These are only useful for testing, and our test harness has a internal
Go API that removes the need to have this functionality exposed as a
subcommand.

[codecov]

Codecov Report

Merging #2492 into master will increase coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2492      +/-   ##
==========================================
+ Coverage   67.33%   67.48%   +0.15%     
==========================================
  Files         322      321       -1     
  Lines       29809    29768      -41     
==========================================
+ Hits        20071    20090      +19     
+ Misses       7292     7231      -61     
- Partials     2446     2447       +1

Impacted Files	Coverage Δ
go/oasis-node/cmd/debug/debug.go	100% <ø> (ø)	⬆️
go/worker/compute/committee/state.go	74.07% <0%> (-11.12%)	⬇️
go/worker/common/p2p/p2p.go	62.61% <0%> (-8.56%)	⬇️
go/common/cbor/codec.go	64.7% <0%> (-5.89%)	⬇️
go/worker/common/host/protocol/protocol.go	65.67% <0%> (-5.23%)	⬇️
go/worker/compute/committee/node.go	61.97% <0%> (-4.63%)	⬇️
go/worker/common/committee/group.go	80.07% <0%> (-2.26%)	⬇️
go/consensus/tendermint/abci/mux.go	67.39% <0%> (-0.73%)	⬇️
go/roothash/api/commitment/pool.go	70.91% <0%> (-0.6%)	⬇️
go/storage/client/client.go	70.65% <0%> (+0.72%)	⬆️
... and 11 more

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