remove obsolete comment in AtEOXact_Inval

Hi, Hackers,

When I read the code, I noticed there is one line of comment in function AtEOXact_Inval() which is obviously obsolete.

    "This should be called as the last step in processing a transaction"

AtEOXact_Inval() is called in CommitTransaction() and AbortTransaction() and there are many other steps after function AtEOXact_Inval() is called.
Such as:
      AtCommit_Notify();
      AtEOXact_GUC(true, 1);
      AtEOXact_SPI(true);
      AtEOXact_Enum();
      AtEOXact_on_commit_actions(true);
      AtEOXact_Namespace(true, is_parallel_worker);
      AtEOXact_SMgr();
      AtEOXact_Files(true);
      AtEOXact_ComboCid();
      AtEOXact_HashTables(true);
      AtEOXact_PgStat(true, is_parallel_worker);
      AtEOXact_Snapshot(true, false);
      AtEOXact_ApplyLauncher(true);
      AtEOXact_LogicalRepWorkers(true);

So that comment is no longer true. I made a patch to remove it as attached.

Best Regards,
Steven