Remove the RETRYABLE failure mode from the exporter interfaces.

[jkwatson]

With the merging of open-telemetry/opentelemetry-specification#511, this should get us into spec compliance.

[codecov-io]

Codecov Report

Merging #1112 into master will increase coverage by 0.14%.
The diff coverage is 81.81%.

@@             Coverage Diff              @@
##             master    #1112      +/-   ##
============================================
+ Coverage     85.58%   85.73%   +0.14%     
+ Complexity     1085     1081       -4     
============================================
  Files           138      138              
  Lines          3990     3974      -16     
  Branches        355      351       -4     
============================================
- Hits           3415     3407       -8     
+ Misses          434      426       -8     
  Partials        141      141              

Impacted Files	Coverage Δ	Complexity Δ
...metry/exporters/jaeger/JaegerGrpcSpanExporter.java	63.23% <0.00%> (+3.51%)	4.00 <0.00> (ø)
...metry/exporters/inmemory/InMemorySpanExporter.java	100.00% <100.00%> (ø)	7.00 <0.00> (ø)
...lemetry/exporters/otlp/OtlpGrpcMetricExporter.java	82.75% <100.00%> (+3.97%)	5.00 <0.00> (-1.00)	⬆️
...telemetry/exporters/otlp/OtlpGrpcSpanExporter.java	82.75% <100.00%> (+3.97%)	5.00 <0.00> (-1.00)	⬆️
...entelemetry/sdk/metrics/export/MetricExporter.java	100.00% <100.00%> (ø)	0.00 <0.00> (ø)
...ntelemetry/sdk/trace/export/MultiSpanExporter.java	100.00% <100.00%> (ø)	10.00 <0.00> (-2.00)
...o/opentelemetry/sdk/trace/export/SpanExporter.java	100.00% <100.00%> (ø)	0.00 <0.00> (ø)

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