infra: remove generate contrib workflows from core #643

Job	Run time
opentelemetry-api	38s
opentelemetry-getting-started	52s
opentelemetry-opentracing-shim	40s
opentelemetry-proto-protobuf5	28s
opentelemetry-sdk	44s
opentelemetry-semantic-conventions	38s
opentelemetry-exporter-opencensus	38s
opentelemetry-exporter-otlp-combined	44s
opentelemetry-exporter-otlp-proto-common	38s
opentelemetry-exporter-otlp-proto-grpc	43s
opentelemetry-exporter-otlp-proto-http	40s
opentelemetry-exporter-prometheus	35s
opentelemetry-exporter-zipkin-combined	36s
opentelemetry-exporter-zipkin-json	47s
opentelemetry-exporter-zipkin-proto-http	39s
opentelemetry-opencensus-shim	40s
opentelemetry-propagator-b3	35s
opentelemetry-propagator-jaeger	34s
opentelemetry-test-utils	33s
	12m 22s

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