Prior to this patch, logging via a secondary logger would allocate a
buffer, then add it to the buffer free list of the secondary logger.

This was causing a memory leak because only the free list from the
main logger is used to allocate buffers (even in secondary loggers),
so all the now-unused buffers from secondary logs would remain unused
and accumulate, locked from Go's GC attention because they are
referenced somewhere.

Release justification: bug fix

Release note (bug fix): A memory leak was fixed that affected
secondary logging (SQL audit logs, statement execution, and RocksDB
logging).