fix: don't mention retrying in the database connection error message

The PGRST000 database connection error message was "Database connection
error. Retrying the connection.", but reconnection attempts are already
logged separately by the reconnection observation, and on fatal errors
(e.g. authentication failure) PostgREST does not retry at all. Drop the
"Retrying the connection." part, leaving "Database connection error.".

src/PostgREST/Error.hs

@@ -541,7 +541,7 @@ instance ErrorBody SQL.UsageError where
   code    (SQL.SessionUsageError (SQL.QueryError _ _ e)) = code e
   code    SQL.AcquisitionTimeoutUsageError               = "PGRST003"
 
-  message (SQL.ConnectionUsageError _) = "Database connection error. Retrying the connection."
+  message (SQL.ConnectionUsageError _) = "Database connection error."
   message (SQL.SessionUsageError (SQL.QueryError _ _ e)) = message e
   message SQL.AcquisitionTimeoutUsageError = "Timed out acquiring connection from connection pool."