Remove exponential backoff code from all plugins

[PettitWesley]

When I built the Firehose and CloudWatch plugins, I thought it would be a good idea for them to implement backoff in case of API throttling. That instinct was good, but the execution shows my lack of understanding of Fluent Bit at the time. Fluent Bit has it's own retry mechanisms; a plugin can return FLB_RETRY and let Fluent Bit handle it. More importantly, the backoff mechanism in use currently causes the plugin to sleep- since Fluent Bit is single-threaded, but concurrent, this sleep stops all other plugins, and thus impacts its overall performance.

In practice I suspect few users trigger throttling; however, this is a very easy thing to fix, we just need to remove a bit of code from all the plugins.