Delete txn scope code

[ekexium]

Part of pingcap/tidb#58838

Some changes that I'm not sure about:

1. Test TestMinSafeTsFromMixed1 and TestMinSafeTsFromMixed2
2. updateGlobalTxnScopeTSFromPD

[cfzjywxk]

@JmPotato PTAL

[ekexium]

any plan to deprecate (or rename) oracle.GlobalTxnScope?

Yes, I think it's the last step. After we deprecated txn-scope related code, we can rename those left to names like ReadReplicaScope

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cfzjywxk, zyguan

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[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2025-03-06 07:36:42.769818444 +0000 UTC m=+513515.898738189: :ballot_box_with_check: agreed by zyguan.
• 2025-03-14 09:38:26.942358331 +0000 UTC m=+2800.626594429: :ballot_box_with_check: agreed by cfzjywxk.
• 2025-09-10 07:55:44.718158456 +0000 UTC m=+434411.278039963: :heavy_multiplication_x::repeat: reset by ekexium.

[ti-chi-bot[bot]]

New changes are detected. LGTM label has been removed.

[you06]

You can ignore the leak goroutine to fix the test.

https://github.com/tikv/client-go/blob/469a7adf7ae88ce8ac69f49473f0b82324030f0b/integration_tests/main_test.go#L27-L31

	opts := []goleak.Option{
		goleak.IgnoreTopFunction("github.com/pingcap/goleveldb/leveldb.(*DB).mpoolDrain"),
		goleak.IgnoreTopFunction("github.com/tikv/client-go/v2/txnkv/transaction.keepAlive"), // TODO: fix ttlManager goroutine leak
		goleak.IgnoreTopFunction("github.com/tikv/client-go/v2/config/retry.(*Config).createBackoffFn.newBackoffFn.func2"),
+		goleak.IgnoreTopFunction("go.opencensus.io/stats/view.(*worker).start"),
	}