Remove the legacy query planner

.changesets/maint_simon_unbridge.md

@@ -0,0 +1,11 @@
+### Remove the legacy query planner ([PR #6418](https://github.com/apollographql/router/pull/6418))
+
+The legacy query planner has been removed in this release. In the previous release, Router 1.58, it was already no longer used by default but it was still available through the `experimental_query_planner_mode`  configuration key. That key is now removed.
+
+Also removed are configuration keys which were only relevant to the legacy planner:
+
+* `supergraph.query_planning.experimental_parallelism`: the new planner can always use available parallelism.
+* `supergraph.experimental_reuse_query_fragments`: this experimental algorithm that attempted to
+reuse fragments from the original operation while forming subgraph requests is no longer present. Instead, by default new fragment definitions are generated based on the shape of the subgraph operation.
+
+By [@SimonSapin](https://github.com/SimonSapin) in https://github.com/apollographql/router/pull/6418

.config/nextest.toml

@@ -118,7 +118,6 @@ or ( binary_id(=apollo-router::integration_tests) & test(=integration::redis::en
 or ( binary_id(=apollo-router::integration_tests) & test(=integration::redis::query_planner_redis_update_defer) )
 or ( binary_id(=apollo-router::integration_tests) & test(=integration::redis::query_planner_redis_update_introspection) )
 or ( binary_id(=apollo-router::integration_tests) & test(=integration::redis::query_planner_redis_update_query_fragments) )
-or ( binary_id(=apollo-router::integration_tests) & test(=integration::redis::query_planner_redis_update_reuse_query_fragments) )
 or ( binary_id(=apollo-router::integration_tests) & test(=integration::redis::query_planner_redis_update_type_conditional_fetching) )
 or ( binary_id(=apollo-router::integration_tests) & test(=integration::redis::test::connection_failure_blocks_startup) )
 or ( binary_id(=apollo-router::integration_tests) & test(=integration::subgraph_response::test_invalid_error_locations_contains_negative_one_location) )

CONTRIBUTING.md

@@ -51,8 +51,6 @@ Refer to [the README file](README.md) or run `cargo run --help` for more informa
 
 - `crates/apollo-router/src/main.rs`: the entry point for the executable
 
-Some of the functionalities rely on the current Javascript / TypeScript implementation, provided by [apollo federation](https://github.com/apollographql/federation), which is exposed through the [federation router-bridge](https://github.com/apollographql/federation/tree/main/router-bridge).
-
 ## Documentation
 
 Documentation for using and contributing to the Apollo Router Core is built using Gatsby