Revert "rust: bump untrusted from 0.7.1 to 0.8.0"

[kostko]

Reverting as untrusted 0.8.0 has been yanked, see briansmith/untrusted#57.

This reverts commit f80896d.

[codecov]

Codecov Report

Merging #3919 (a337b41) into master (4c0f42e) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #3919      +/-   ##
==========================================
- Coverage   67.01%   67.00%   -0.02%     
==========================================
  Files         405      405              
  Lines       41266    41266              
==========================================
- Hits        27656    27649       -7     
- Misses       9659     9670      +11     
+ Partials     3951     3947       -4     

Impacted Files	Coverage Δ
go/oasis-node/cmd/common/metrics/disk.go	65.38% <0.00%> (-19.24%)	⬇️
go/oasis-node/cmd/common/metrics/resource.go	78.94% <0.00%> (-10.53%)	⬇️
go/consensus/tendermint/abci/state/state.go	54.54% <0.00%> (-9.10%)	⬇️
go/consensus/tendermint/apps/beacon/genesis.go	62.50% <0.00%> (-6.25%)	⬇️
go/common/sgx/common.go	58.53% <0.00%> (-4.88%)	⬇️
go/storage/api/root_cache.go	75.55% <0.00%> (-4.45%)	⬇️
go/consensus/tendermint/apps/beacon/beacon.go	71.73% <0.00%> (-4.35%)	⬇️
go/consensus/tendermint/full/services.go	80.00% <0.00%> (-4.17%)	⬇️
go/consensus/tendermint/apps/beacon/state/state.go	71.42% <0.00%> (-3.18%)	⬇️
go/storage/database/database.go	75.22% <0.00%> (-1.84%)	⬇️
... and 28 more

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