Cleanup data from the InvoiceEvents table

[NicolasDorier]

This PR save 43% of space in the biggest table in BTCPay Server's schema without deleting any useful data.

An unused 10-byte UniqueId column is included in every line of logs. This column was originally required to satisfy Entity Framework, but by switching to Dapper, we can eliminate it and save 20 bytes per log line (including index and table data).

VACUUM FULL ensures that the space of the removed column is reclaimed by the OS.
ANALYZE ensures that the new index get used.

Table Name	Total Size	Index Size	Table Size
InvoiceEvents2	926 MB	352 MB	573 MB

To

Table Name	Total Size	Index Size	Table Size
InvoiceEvents2	529 MB	42 MB	486 MB

Incidentally, the code is more concise.