remove unneeded pstrdup in fetch_table_list

Hi

In function fetch_table_list, it get the table names from publicer and return a list of tablenames.
When append the name to the list, it use the following code:

**
    nspname = TextDatumGetCString(slot_getattr(slot, 1, &isnull));
    Assert(!isnull);
    relname = TextDatumGetCString(slot_getattr(slot, 2, &isnull));
    rv = makeRangeVar(pstrdup(nspname), pstrdup(relname), -1);
    tablelist = lappend(tablelist, rv);
**

the nspname and relname will be copied which seems unnecessary.
Because nspame and relname is get from TextDatumGetCString.
IMO, TextDatumGetCString returns a newly palloced string.

**
    result = (char *) palloc(len + 1);
    memcpy(result, VARDATA_ANY(tunpacked), len);
    result[len] = '\0';

    if (tunpacked != t)
        pfree(tunpacked);

    return result;
**

It may harm when there are a lot of tables are replicated.
So I try to fix this.

Best regards,
houzj