Revert "Header-only sync for old forks (#3942)" (#4022)

substrate/core/client/db/src/lib.rs

substrate/core/client/src/client.rs

substrate/core/consensus/common/src/block_import.rs

substrate/core/consensus/common/src/import_queue.rs

substrate/core/finality-grandpa/src/light_import.rs

substrate/core/finality-grandpa/src/tests.rs

substrate/core/network/src/protocol/sync.rs

substrate/core/network/src/test/block_import.rs

substrate/core/network/src/test/mod.rs

substrate/core/network/src/test/sync.rs

substrate/core/test-client/src/lib.rs