nix: only json output for postgrest-dump-schema

nix/tools/tests.nix

@@ -91,10 +91,7 @@ let
     checkedShellScript
       {
         name = "postgrest-dump-schema";
-        docs = "Dump the loaded schema's SchemaCache in JSON or Yaml format.";
-        args = [
-          "ARG_OPTIONAL_BOOLEAN([yaml], [y], [Dump the schema cache in Yaml format])"
-        ];
+        docs = "Dump the loaded schema's SchemaCache in JSON format.";
         workingDir = "/";
         withEnv = postgrest.env;
         withPath = [ jq ];
@@ -102,8 +99,7 @@ let
       ''
         ${withTools.withPg} -f test/spec/fixtures/load.sql \
             ${cabal-install}/bin/cabal v2-run ${devCabalOptions} --verbose=0 -- \
-            postgrest --dump-schema \
-            | if [ "$_arg_yaml" = on ]; then ${yq}/bin/yq -y .; else cat; fi
+            postgrest --dump-schema
       '';
 
   coverage =