Revert "SERVER-120914 UnshardCollection now fails with NamespaceNotSharded for untracked collections (#49130)" (#49219)

Co-authored-by: auto-revert-processor <devprod-si-team@mongodb.com>
GitOrigin-RevId: c9a2e7dd02bb7055136848a0dbd7cdb9a262bfb7

etc/backports_required_for_multiversion_tests.yml

@@ -149,8 +149,6 @@ last-continuous:
       ticket: SERVER-112273
     - test_file: jstests/replsets/retryable_write_interrupted_on_stepdown.js
       ticket: SERVER-110728
-    - test_file: jstests/sharding/unshard_collection_basic.js
-      ticket: SERVER-120914
   suites: null
 last-lts:
   all:
@@ -798,6 +796,4 @@ last-lts:
       ticket: SERVER-112273
     - test_file: jstests/replsets/retryable_write_interrupted_on_stepdown.js
       ticket: SERVER-110728
-    - test_file: jstests/sharding/unshard_collection_basic.js
-      ticket: SERVER-120914
   suites: null

jstests/sharding/unshard_collection_basic.js

@@ -49,7 +49,7 @@ const unshardedCollName = "foo_unsharded";
 const unshardedCollNS = dbName + "." + unshardedCollName;
 assert.commandWorked(st.s.getDB(dbName).runCommand({create: unshardedCollName}));
 let res = mongos.adminCommand({unshardCollection: unshardedCollNS});
-assert.commandFailedWithCode(res, ErrorCodes.NamespaceNotSharded);
+assert.commandFailedWithCode(res, [ErrorCodes.NamespaceNotFound, ErrorCodes.NamespaceNotSharded]);
 
 jsTest.log("Verify unshardCollection succeeds with explicit toShard option");
 let coll = mongos.getDB(dbName)[collName];

src/mongo/db/s/resharding/reshard_collection_coordinator.cpp

@@ -149,21 +149,6 @@ ExecutorFuture<void> ReshardCollectionCoordinator::_runImpl(
                 Grid::get(opCtx)->catalogCache()->getCollectionPlacementInfoWithRefresh(opCtx,
                                                                                         nss()));
 
-            // For unshardCollection on untracked collections that exist locally, return
-            // NamespaceNotSharded. Non-existent collections fall through to NamespaceNotFound
-            // below. Tracked-unsplittable collections are handled downstream for idempotency.
-            if (resharding::isUnshardCollection(_doc.getProvenance()) && !cmOld.hasRoutingTable()) {
-                auto coll = acquireCollectionMaybeLockFree(
-                    opCtx,
-                    CollectionAcquisitionRequest::fromOpCtx(
-                        opCtx, nss(), AcquisitionPrerequisites::kRead));
-                if (coll.exists()) {
-                    uasserted(ErrorCodes::NamespaceNotSharded,
-                              str::stream() << "Collection '" << nss().toStringForErrorMsg()
-                                            << "' is not sharded.");
-                }
-            }
-
             uassert(ErrorCodes::NamespaceNotFound,
                     str::stream() << "Collection '" << nss().toStringForErrorMsg()
                                   << "' not found in cluster catalog",