Remove hydra-explorer from this repo #6146

Job	Run time
Benchmarks (hydra-node, tx-cost, --output-directory $(pwd)/../benchmarks)	2m 9s
Benchmarks (hydra-node, micro, -o $(pwd)/../benchmarks/ledger-bench.html)	1m 57s
Benchmarks (hydra-cluster, bench-e2e, datasets datasets/1-node.json datasets/3-nodes.json --outpu...	6m 15s
Build specification using nix	1m 46s
Build & test (hydra-plutus)	1m 50s
Build haddock using nix	3m 56s
Build & test (hydra-tui)	6m 55s
nix flake check	5m 12s
Build & test (hydra-node)	7m 5s
Build & test (hydra-tx)	2m 3s
Compute cost differences	3m 12s
Build & test (hydra-cluster)	11m 57s
Publish benchmark results	3s
Documentation	2m 34s
Publish test results	11s
	57m 5s

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