Set null to Session.transactionId explicitly when create from other Session

[takezoe]

Description

No need of copying Session.transactionId when it's created from other Session because it's always null as it's checked in advance here:

trino/core/trino-main/src/main/java/io/trino/Session.java

Line 722 in de9553b

checkArgument(session.getTransactionId().isEmpty(), "Session builder cannot be created from a session in a transaction");

Additional context and related issues

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## Section
* Fix some things. ({issue}`issuenumber`)