refactor(query-engine): remove legacy SimpleMapStore implementations (#625)

Legacy stores and their comparison benchmark were gated behind a feature
flag but broke cargo clippy pre-commit; deleting them outright removes
the flag and the failure.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

Author: milindsrivastava1997

asap-query-engine/Cargo.toml

@@ -84,11 +84,6 @@ path = "src/bin/e2e_quickstart_resource_test.rs"
 tempfile = "3.20.0"
 criterion = { version = "0.5", features = ["html_reports"] }
 
-[[bench]]
-name = "simple_store_bench"
-harness = false
-required-features = ["legacy_stores"]
-
 [features]
 #default = ["lock_profiling", "extra_debugging"]
 default = ["jemalloc"]
@@ -98,8 +93,3 @@ jemalloc = ["dep:tikv-jemallocator"]
 lock_profiling = []
 # Enable extra debugging output
 extra_debugging = []
-# Legacy SimpleMapStore implementations, kept only for the simple_store_bench
-# comparison benchmark. Off by default so the Store trait's real implementors
-# are just SimpleMapStoreGlobal/PerKey — adding a Store trait method doesn't
-# require updating the legacy variants.
-legacy_stores = []