Always delete the 901 field from incoming MARC records;

Always delete the 901 field from incoming MARC records;
we append a new 901 with the TCN and read from it, so
there can be only one 901. Well - we could read from the
last 901 in a list of returned fields, but that's not
our current style.

Use 'exists' test to avoid autovivifying hashes for a tiny
amount of overall saving of memory.

If no start ID is supplied at the command line, get the
next biblio.record_entry ID value from the database.

Remove references to the $start_id variable; it is unused.

git-svn-id: svn://svn.open-ils.org/ILS/trunk@7934 dcc99617-32d9-48b4-a31d-7c20da2025e4