go/runtime: Fix configuring the SGX-based provisioner

[kostko]

Previously there was an edge case when the SGX loader was configured and remapping to non-SGX was forced (e.g. on client nodes). This would result in an invalid SGX configuration that resulted in a strange error message about a missing SIGSTRUCT.

This has now been changed so that remapping happens independent of whether an SGX loader is configured or not.

[codecov]

Codecov Report

Merging #4960 (55e7797) into master (84a3e9b) will increase coverage by 0.01%.
The diff coverage is 25.00%.

❗ Current head 55e7797 differs from pull request most recent head 5f57c69. Consider uploading reports for the commit 5f57c69 to get more accurate results

@@            Coverage Diff             @@
##           master    #4960      +/-   ##
==========================================
+ Coverage   66.64%   66.66%   +0.01%     
==========================================
  Files         464      464              
  Lines       51226    51228       +2     
==========================================
+ Hits        34141    34150       +9     
+ Misses      12885    12883       -2     
+ Partials     4200     4195       -5     

Impacted Files	Coverage Δ
go/runtime/host/sgx/sgx.go	72.00% <0.00%> (-0.73%)	⬇️
go/runtime/registry/config.go	70.15% <33.33%> (ø)
go/storage/mkvs/lookup.go	75.00% <0.00%> (-4.17%)	⬇️
...consensus/tendermint/apps/roothash/transactions.go	66.66% <0.00%> (-3.12%)	⬇️
go/oasis-node/cmd/stake/delegations.go	78.99% <0.00%> (-1.69%)	⬇️
...consensus/tendermint/apps/registry/transactions.go	54.60% <0.00%> (-1.64%)	⬇️
go/consensus/tendermint/abci/state.go	74.28% <0.00%> (-1.43%)	⬇️
.../consensus/tendermint/apps/registry/state/state.go	60.55% <0.00%> (-1.12%)	⬇️
go/worker/compute/executor/committee/node.go	69.79% <0.00%> (-0.99%)	⬇️
go/registry/api/api.go	57.46% <0.00%> (-0.76%)	⬇️
... and 12 more

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