Normalize name of KeyDate elements in Music at Columbia

In the remediated metadata for Music at Columbia, the KeyDate columns
had different names compared to the previous collection that were
remediated:
item_-_MODS_-_KeyDate_1 was used instead of item_-_MODS_-_KeyDate_-_Single_Start
and item_-_MODS_-_KeyDate_2 was used instead of item_-_MODS_-_KeyDate_-_End
So, replace the unexpected element names with the usual ones.
Regenerate MODS due to change in column name remediated metadata

In the remediated metadata for Music at Columbia, the KeyDate columns
had different names compared to the previous collection that were
remediated:
item_-_MODS_-_KeyDate_1 was used instead of item_-_MODS_-_KeyDate_-_Single_Start
and item_-_MODS_-_KeyDate_2 was used instead of item_-_MODS_-_KeyDate_-_End
So, replace the unexpected element names with the usual ones.