Remove redundant Assert in localXidSatisfiesAnyDistributedSnapshot.

Right below we have an if-statement to check the same thing as
this assert.

src/backend/cdb/cdbdistributedsnapshot.c

@@ -51,7 +51,6 @@ bool
 localXidSatisfiesAnyDistributedSnapshot(TransactionId localXid)
 {
 	DistributedSnapshotCommitted distributedSnapshotCommitted;
-	Assert(TransactionIdIsNormal(localXid));
 
 	/*
 	 * In general expect this function to be called only for normal xid, as

src/test/regress/expected/vacuum_gp.out

+-- Test vacuum a catalog can succeed.
+-- Previously, we have a redundant Assert in the function
+-- localXidSatisfiesAnyDistributedSnapshot that will fail this.
+-- See Github Issue 6793.
+vacuum full pg_proc;
 set optimizer_print_missing_stats = off;
 -- MPP-23647 Create a partitioned appendonly table, let its age
 -- increase during the test.  We will vacuum it at the end of the

src/test/regress/sql/vacuum_gp.sql

+-- Test vacuum a catalog can succeed.
+-- Previously, we have a redundant Assert in the function
+-- localXidSatisfiesAnyDistributedSnapshot that will fail this.
+-- See Github Issue 6793.
+vacuum full pg_proc;
+
 set optimizer_print_missing_stats = off;
 -- MPP-23647 Create a partitioned appendonly table, let its age
 -- increase during the test.  We will vacuum it at the end of the