token_metadata_impl: clear_gently: release version tracker early

No need to wait for all members to be cleared gently.
We can release the version earlier since the
held version may be awaited for in barriers.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>

locator/token_metadata.cc

@@ -357,6 +357,7 @@ future<std::unique_ptr<token_metadata_impl>> token_metadata_impl::clone_only_tok
 }
 
 future<> token_metadata_impl::clear_gently() noexcept {
+    _version_tracker = {};
     co_await utils::clear_gently(_token_to_endpoint_map);
     co_await utils::clear_gently(_normal_token_owners);
     co_await utils::clear_gently(_bootstrap_tokens);