Remove exponential backoff code

[PettitWesley]

Issue #, if available:
aws/amazon-kinesis-firehose-for-fluent-bit#23
fluent/fluent-bit#2159

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[hencrice]

Any tests need to be updated?

[sonofachamp]

Do we need to return an FLB_RETRY in place of the previous calls to backoff functionality?

[zackwine]

You'll need to update the kinesis_test.go file as well: https://github.com/aws/amazon-kinesis-streams-for-fluent-bit/blob/master/kinesis/kinesis_test.go#L43

[PettitWesley]

@zackwine @hencrice Good point... I ran the integ tests but forgot to check the unit tests

@sonofachamp Yeah, you're right.