Remove logging of DB connection pooling.
Remove logging of DB connection pooling.

This assumes `.get_backend_pid()` is always available, which may not
be the case -- and in general is confusing behavior for a library:
verbose logging should be somehow activated by library clients, not be
"on" by default.

TissueMAPS/TmLibrary,TissueMAPS/TmLibrary,TissueMAPS/TmLibrary,TissueMAPS/TmLibrary,TissueMAPS/TmLibrary