Update xml format to match the mock ligo.skymap's coinc.xml
In the mock coinc.xml shown at: https://lscsoft.docs.ligo.org/ligo.skymap/interface.html#event-data https://lscsoft.docs.ligo.org/ligo.skymap/_downloads/9663428149cff1414ea2c22f8b7db788/coinc.xml
Column names do not include the table name as a prefix.
Uninitialized values are empty instead of zero or a default timestamp.