Remove hydra-explorer from this repo (#1736)

This removes the hydra-explorer from this repo; and needs to be merged
in combination with
cardano-scaling/hydra-explorer#5.

Note that there was one set of tests in the `hydra-cluster` tool that
depended on the explorer; I've had to then remove those here, but am not
yet sure if I can get them to work over on the other side.

Todo:

- [ ] Update changelog
- [ ] Check for references in the docs
- [ ] ???

.github/workflows/docker.yaml

@@ -21,7 +21,7 @@ jobs:
   docker:
     strategy:
       matrix:
-        target: [ hydra-node, hydra-tui, hydraw, hydra-explorer ]
+        target: [ hydra-node, hydra-tui, hydraw ]
 
     runs-on: ubuntu-latest
     steps:

cabal.project

@@ -27,7 +27,6 @@ packages:
   hydra-tui
   hydraw
   hydra-chain-observer
-  hydra-explorer
 
 -- Compile more things in parallel
 package *

flake.nix

@@ -172,7 +172,6 @@
             "hydra-cardano-api"
             "hydra-chain-observer"
             "hydra-cluster"
-            "hydra-explorer"
             "hydra-node"
             "hydra-tx"
             "hydra-plutus"

hydra-cluster/hydra-cluster.cabal

@@ -153,7 +153,6 @@ test-suite tests
     Test.Hydra.Cluster.FaucetSpec
     Test.Hydra.Cluster.MithrilSpec
     Test.Hydra.Cluster.Utils
-    Test.HydraExplorerSpec
     Test.OfflineChainSpec
 
   build-depends:
@@ -167,11 +166,8 @@ test-suite tests
     , filepath
     , hspec
     , hspec-golden-aeson
-    , http-client
-    , http-conduit
     , hydra-cardano-api
     , hydra-cluster
-    , hydra-explorer
     , hydra-node
     , hydra-node:testlib
     , hydra-prelude
@@ -190,7 +186,6 @@ test-suite tests
   build-tool-depends:
     , hspec-discover:hspec-discover
     , hydra-chain-observer:hydra-chain-observer
-    , hydra-explorer:hydra-explorer
     , hydra-node:hydra-node
 
   ghc-options:        -threaded -rtsopts