LP932540: Fix ISSN indexing

LP932540: Fix ISSN indexing

The default config.metabib_field_index_norm_map contains a 'replace'
entry for the ISSN identifier field that replaces spaces with "". That
was meant to handle ISSNs that incorrectly contain a space instead of a
hyphen; it normalizes them from: "1234 1234" to "12341234".

However, that breaks indexing ISSNs if there are multiple ISSNs in the
record, or even if there is an extra character in the same subfield as
the primary ISSN, as all spaces are removed.

This commit removes the 'replace' entry for the ISSN identifier field
and reindexes potentially damaged ISSN index entries.

Signed-off-by: Dan Scott <dan@coffeecode.net>