Remove useless casts of vsnprintf() return value.
Remove useless casts of vsnprintf() return value.

The return value is not checked because we are happy with a truncated result in this case, which is guaranteed by passing the buffer size.

Found on MacOS M1.

pgmasters/backrest,pgbackrest/pgbackrest,pgmasters/backrest,pgbackrest/pgbackrest,pgbackrest/pgbackrest