CBG-5499 Remove dead non-xattr code used for query

[torcolvin]

CBG-5499 Remove dead non-xattr code used for query

Sync Gateway only supports enable_shared_bucket_access / xattrs since 4.0. Remove dead code. I left the index definitions to drop in the index names to make it clear that they were not changing.

Pre-review checklist

• Removed debug logging (fmt.Print, log.Print, ...)
• Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Integration Tests

• https://jenkins.sgwdev.com/job/SyncGatewayIntegration/878/

[Copilot]

Pull request overview

This PR removes legacy non-xattr query/index code paths and associated test branching, aligning index/query generation with Sync Gateway 4.0+ where xattrs are required. It simplifies index naming/token replacement by eliminating the UseXattrs parameter plumbing and standardizing on _xN index variants while still testing cleanup of old _1 indexes during post-upgrade.

Changes:

• Remove UseXattrs-based branching from index/query token replacement and index option plumbing.
• Standardize tests to expect _x1 index names and always enable xattrs in relevant configs.
• Update post-upgrade index cleanup tests to explicitly create old non-xattr (*_1) indexes and verify they’re removed.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
rest/server_context.go	Stop passing UseXattrs into legacy-index selection; rely on xattrs-only behavior.
rest/indextest/post_upgrade_test.go	Remove non-xattr branches from REST post-upgrade index tests; keep expected removed index names stable.
rest/indextest/index_test.go	Hardcode _x1 index expectations and remove non-xattr skips/branches in index tests.
rest/indextest/index_init_api_test.go	Simplify index-init API tests to xattrs-only index suffix handling.
rest/database_init_manager.go	Remove UseXattrs from constructed index initialization options.
db/util_testing.go	Remove UseXattrs from test bucket/index initialization options.
db/query.go	Remove non-xattr token replacement paths in N1QL query statement construction.
db/query_test.go	Update query coverage test to use xattrs-only token/index replacement signatures.
db/indextest/util.go	Remove xattr toggle from index test helper options; add helper to create legacy non-xattr index names.
db/indextest/post_upgrade_test.go	Rewrite upgrade/removal tests to xattrs-only runtime while simulating old _1 indexes for cleanup verification.
db/indextest/indextest_test.go	Remove non-xattr matrix cases and update index expectations to xattrs-only naming.
db/indextest/indextest_dual_metadata_test.go	Remove UseXattrs from index initialization options in dual-metadata tests.
db/indexes.go	Remove non-xattr sync token/index naming logic and UseXattrs from index options/signatures.
db/database.go	Remove UseXattrs from in-use index computation options.
db/background_mgr_resync_dcp.go	Remove UseXattrs from principal-index initialization options.