implicitly_retry_on_database_drop_pending.js calls tojson() inside of a loop

// We filter out operations that didn't produce a write error to avoid causing a

// duplicate key error when retrying the operations.

for (let writeError of res.writeErrors) {

    assert.lt(writeError.index,

              opsExecuted.length,

              "A write error was returned for an operation outside the list" +

                  " of operations executed: " + tojson(res));

    opsToRetry.push(opsExecuted[writeError.index]);

}