Fix: Remove implementation of `Instant` for `std::time::Instant` #332

Job	Run time
cluster-benchmark (cluster_benchmark)	45s
openraft-feature-test (nightly)	52s
openraft-feature-test (nightly, serde)	50s
openraft-test (stable, 0)	2m 58s
external-stores (stores/rocksstore-v2)	6m 2s
openraft-feature-test (nightly, single-term-leader)	47s
openraft-test (nightly, 30)	3m 17s
openraft-feature-test (nightly, single-term-leader,serde,singlethreaded)	51s
openraft-test (nightly, 0, single-term-leader)	3m 4s
openraft-test-bench (nightly)	53s
stores (memstore)	55s
Build (nightly, bench,serde,bt,singlethreaded)	48s
stores (rocksstore)	5m 54s
stores (rocksstore-compat07)	6m 3s
tests-feature-test (nightly)	2m 46s
stores (sledstore)	1m 0s
examples (stable, raft-kv-memstore)	2m 30s
tests-feature-test (nightly, single-term-leader)	2m 48s
examples (stable, raft-kv-memstore-singlethreaded)	1m 6s
tests-feature-test (nightly, loosen-follower-log-revert)	2m 55s
examples (stable, raft-kv-rocksdb)	8m 0s
lint	6m 32s
examples (nightly, raft-kv-memstore)	2m 9s
examples (nightly, raft-kv-memstore-singlethreaded)	1m 17s
examples (nightly, raft-kv-rocksdb)	12m 14s
	1h 17m 16s

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