docker: remove docker image build and cleanup images

[ptrus]

With oasislabs/oasis-ethwasi-runtime#985 the docker image built from Oasis Core is not needed anymore. This PR can be merged, but the buildkite pipeline itself should not be deleted until the Oasis Runtime PR is merged.

• Removes deployment related docker stuff
• cleans up testing dockerifle

TODO:

• test (also needs to be tested in oasis-runtime pipeline)
• update existing oasislabs/testing:0.3.0 image (after this is approved and ready to merge)

[codecov]

Codecov Report

Merging #2838 into master will increase coverage by 0.19%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2838      +/-   ##
==========================================
+ Coverage   67.27%   67.47%   +0.19%     
==========================================
  Files         344      344              
  Lines       33089    33089              
==========================================
+ Hits        22262    22328      +66     
+ Misses       7924     7887      -37     
+ Partials     2903     2874      -29     

Impacted Files	Coverage Δ
go/common/cbor/codec.go	77.14% <0.00%> (-5.72%)	⬇️
go/worker/storage/service_external.go	47.31% <0.00%> (-4.31%)	⬇️
go/consensus/tendermint/roothash/roothash.go	68.91% <0.00%> (-2.63%)	⬇️
go/worker/common/p2p/p2p.go	64.41% <0.00%> (-1.81%)	⬇️
go/common/grpc/grpc.go	79.42% <0.00%> (-1.24%)	⬇️
go/consensus/tendermint/abci/mux.go	68.91% <0.00%> (-0.46%)	⬇️
go/worker/compute/merge/committee/node.go	75.87% <0.00%> (-0.25%)	⬇️
go/consensus/tendermint/tendermint.go	68.07% <0.00%> (+0.27%)	⬆️
.../consensus/tendermint/apps/registry/state/state.go	61.00% <0.00%> (+0.53%)	⬆️
go/consensus/tendermint/abci/state.go	70.27% <0.00%> (+1.15%)	⬆️
... and 16 more

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