Span events stored as Vector instead of EvictedQueue

[cijothomas]

Continuing from https://github.com/open-telemetry/opentelemetry-rust/pull/1313/files, this one for Events.

Cleanup of unused code (EvictedQueue etc. will be done later.)
IndexMap dependency is also potentially removable, after some more fixes in Loggging side. Expect them as follow ups!

[codecov]

Codecov Report

Attention: 3 lines in your changes are missing coverage. Please review.

Files	Coverage Δ
opentelemetry-datadog/src/exporter/model/mod.rs	85.1% <100.0%> (-0.1%)	⬇️
opentelemetry-sdk/src/export/trace.rs	40.0% <ø> (ø)
opentelemetry-sdk/src/testing/trace/mod.rs	80.8% <100.0%> (ø)
opentelemetry-sdk/src/trace/events.rs	100.0% <100.0%> (ø)
opentelemetry-sdk/src/trace/mod.rs	100.0% <100.0%> (ø)
opentelemetry-sdk/src/trace/span.rs	96.1% <100.0%> (+0.2%)	⬆️
opentelemetry-sdk/src/trace/span_processor.rs	82.8% <100.0%> (ø)
opentelemetry-sdk/src/trace/tracer.rs	94.7% <100.0%> (+<0.1%)	⬆️
opentelemetry-zipkin/src/exporter/model/span.rs	96.1% <100.0%> (ø)
opentelemetry-jaeger/src/exporter/mod.rs	57.3% <0.0%> (ø)
... and 2 more

... and 3 files with indirect coverage changes

📢 Thoughts on this report? Let us know!

[jtescher]

Looks good